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 $141.75   10.486%   $156.6139   $156.61   $156.60   $156.60  
  Purchase #2 $62.48   7.158%   $66.9523   $66.95   $66.95   $67.00  
  Purchase #3 $162.25   11.622%   $181.1067   $181.11   $181.10   $181.10  
  Purchase #4 $158.30   5.379%   $166.815   $166.82   $166.80   $166.80  
  Purchase #5 $113.87   7.195%   $122.0629   $122.06   $122.05   $122.10  
  Purchase #6 $59.27   13.761%   $67.4261   $67.43   $67.45   $67.40  
  Purchase #7 $66.43   13.497%   $75.3961   $75.40   $75.40   $75.40  
  7 purchase totals = $764.35       $836.3730   $836.38   $836.35   $836.40