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 $195.53   6.238%   $207.7272   $207.73   $207.75   $207.70  
  Purchase #2 $93.42   12.688%   $105.2731   $105.27   $105.25   $105.30  
  Purchase #3 $26.69   8.349%   $28.9183   $28.92   $28.90   $28.90  
  Purchase #4 $217.50   12.449%   $244.5766   $244.58   $244.60   $244.60  
  Purchase #5 $94.47   8.684%   $102.6738   $102.67   $102.65   $102.70  
  Purchase #6 $116.65   6.301%   $124.0001   $124.00   $124.00   $124.00  
  Purchase #7 $205.60   7.455%   $220.9275   $220.93   $220.95   $220.90  
  7 purchase totals = $949.86       $1,034.0966   $1,034.10   $1,034.10   $1,034.10