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 $204.58   9.456%   $223.9251   $223.93   $223.95   $223.90  
  Purchase #2 $180.70   11.511%   $201.5004   $201.50   $201.50   $201.50  
  Purchase #3 $196.25   6.513%   $209.0318   $209.03   $209.05   $209.00  
  Purchase #4 $26.78   11.209%   $29.7818   $29.78   $29.80   $29.80  
  Purchase #5 $226.55   5.584%   $239.2006   $239.20   $239.20   $239.20  
  Purchase #6 $246.27   3.268%   $254.3181   $254.32   $254.30   $254.30  
  Purchase #7 $92.76   10.457%   $102.4599   $102.46   $102.45   $102.50  
  7 purchase totals = $1,173.89       $1,260.2177   $1,260.22   $1,260.25   $1,260.20