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 $50.43   12.484%   $56.7257   $56.73   $56.75   $56.70  
  Purchase #2 $232.77   13.320%   $263.775   $263.78   $263.80   $263.80  
  Purchase #3 $66.38   6.571%   $70.7418   $70.74   $70.75   $70.70  
  Purchase #4 $162.78   4.397%   $169.9374   $169.94   $169.95   $169.90  
  Purchase #5 $238.75   11.715%   $266.7196   $266.72   $266.70   $266.70  
  Purchase #6 $20.90   5.319%   $22.0117   $22.01   $22.00   $22.00  
  Purchase #7 $196.85   4.342%   $205.3972   $205.40   $205.40   $205.40  
  7 purchase totals = $968.86       $1,055.3084   $1,055.32   $1,055.35   $1,055.20