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 $72.84   10.638%   $80.5887   $80.59   $80.60   $80.60  
  Purchase #2 $91.33   4.707%   $95.6289   $95.63   $95.65   $95.60  
  Purchase #3 $217.93   7.833%   $235.0005   $235.00   $235.00   $235.00  
  Purchase #4 $163.82   11.557%   $182.7527   $182.75   $182.75   $182.80  
  Purchase #5 $239.61   4.810%   $251.1352   $251.14   $251.15   $251.10  
  Purchase #6 $212.43   11.172%   $236.1627   $236.16   $236.15   $236.20  
  Purchase #7 $123.40   10.783%   $136.7062   $136.71   $136.70   $136.70  
  7 purchase totals = $1,121.36       $1,217.9749   $1,217.98   $1,218.00   $1,218.00