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 $76.39   8.849%   $83.1498   $83.15   $83.15   $83.10  
  Purchase #2 $219.53   6.182%   $233.1013   $233.10   $233.10   $233.10  
  Purchase #3 $120.77   6.313%   $128.3942   $128.39   $128.40   $128.40  
  Purchase #4 $235.51   10.528%   $260.3045   $260.30   $260.30   $260.30  
  Purchase #5 $113.98   4.446%   $119.0476   $119.05   $119.05   $119.00  
  Purchase #6 $98.49   3.538%   $101.9746   $101.97   $101.95   $102.00  
  Purchase #7 $231.76   12.214%   $260.0672   $260.07   $260.05   $260.10  
  7 purchase totals = $1,096.43       $1,186.0392   $1,186.03   $1,186.00   $1,186.00