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 $61.32   9.271%   $67.005   $67.01   $67.00   $67.00  
  Purchase #2 $131.75   6.586%   $140.4271   $140.43   $140.45   $140.40  
  Purchase #3 $186.76   13.768%   $212.4731   $212.47   $212.45   $212.50  
  Purchase #4 $71.89   4.335%   $75.0064   $75.01   $75.00   $75.00  
  Purchase #5 $107.86   9.422%   $118.0226   $118.02   $118.00   $118.00  
  Purchase #6 $68.36   8.261%   $74.0072   $74.01   $74.00   $74.00  
  Purchase #7 $243.93   5.619%   $257.6364   $257.64   $257.65   $257.60  
  7 purchase totals = $871.87       $944.5778   $944.59   $944.55   $944.50