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 $96.65   5.557%   $102.0208   $102.02   $102.00   $102.00  
  Purchase #2 $179.97   7.211%   $192.9476   $192.95   $192.95   $192.90  
  Purchase #3 $203.64   11.306%   $226.6635   $226.66   $226.65   $226.70  
  Purchase #4 $138.39   8.680%   $150.4023   $150.40   $150.40   $150.40  
  Purchase #5 $57.31   10.424%   $63.284   $63.28   $63.30   $63.30  
  Purchase #6 $162.70   4.595%   $170.1761   $170.18   $170.20   $170.20  
  Purchase #7 $48.33   11.271%   $53.7773   $53.78   $53.80   $53.80  
  7 purchase totals = $886.99       $959.2716   $959.27   $959.30   $959.30