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 $7.35   9.667%   $8.0605   $8.06   $8.05   $8.10  
  Purchase #2 $10.46   12.244%   $11.7407   $11.74   $11.75   $11.70  
  Purchase #3 $156.55   13.351%   $177.451   $177.45   $177.45   $177.50  
  Purchase #4 $59.76   5.672%   $63.1496   $63.15   $63.15   $63.10  
  Purchase #5 $86.51   8.399%   $93.776   $93.78   $93.80   $93.80  
  Purchase #6 $56.34   4.668%   $58.97   $58.97   $58.95   $59.00  
  Purchase #7 $58.66   6.137%   $62.26   $62.26   $62.25   $62.30  
  7 purchase totals = $435.63       $475.4078   $475.41   $475.40   $475.50