Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $173.56   11.784%   $194.0123   $194.01   $194.00   $194.00  
  Purchase #2 $224.94   13.311%   $254.8818   $254.88   $254.90   $254.90  
  Purchase #3 $161.80   6.633%   $172.5322   $172.53   $172.55   $172.50  
  Purchase #4 $221.25   11.601%   $246.9172   $246.92   $246.90   $246.90  
  Purchase #5 $190.95   3.706%   $198.0266   $198.03   $198.05   $198.00  
  Purchase #6 $206.71   8.205%   $223.6706   $223.67   $223.65   $223.70  
  Purchase #7 $239.66   7.218%   $256.9587   $256.96   $256.95   $257.00  
  7 purchase totals = $1,418.87       $1,546.9994   $1,547.00   $1,547.00   $1,547.00