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 $40.63   6.619%   $43.3193   $43.32   $43.30   $43.30  
  Purchase #2 $123.93   11.616%   $138.3257   $138.33   $138.35   $138.30  
  Purchase #3 $122.38   9.647%   $134.186   $134.19   $134.20   $134.20  
  Purchase #4 $235.35   13.651%   $267.4776   $267.48   $267.50   $267.50  
  Purchase #5 $104.76   7.304%   $112.4117   $112.41   $112.40   $112.40  
  Purchase #6 $45.35   3.684%   $47.0207   $47.02   $47.00   $47.00  
  Purchase #7 $189.41   11.171%   $210.569   $210.57   $210.55   $210.60  
  7 purchase totals = $861.81       $953.3100   $953.32   $953.30   $953.30