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 $73.80   3.784%   $76.5926   $76.59   $76.60   $76.60  
  Purchase #2 $136.51   6.701%   $145.6575   $145.66   $145.65   $145.70  
  Purchase #3 $46.28   12.281%   $51.9636   $51.96   $51.95   $52.00  
  Purchase #4 $227.86   3.141%   $235.0171   $235.02   $235.00   $235.00  
  Purchase #5 $27.73   3.317%   $28.6498   $28.65   $28.65   $28.60  
  Purchase #6 $227.75   11.107%   $253.0462   $253.05   $253.05   $253.00  
  Purchase #7 $64.47   4.389%   $67.2996   $67.30   $67.30   $67.30  
  7 purchase totals = $804.40       $858.2264   $858.23   $858.20   $858.20