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 $85.42   12.735%   $96.2982   $96.30   $96.30   $96.30  
  Purchase #2 $205.63   12.402%   $231.1322   $231.13   $231.15   $231.10  
  Purchase #3 $128.96   5.545%   $136.1108   $136.11   $136.10   $136.10  
  Purchase #4 $133.35   12.600%   $150.1521   $150.15   $150.15   $150.20  
  Purchase #5 $201.65   13.808%   $229.4938   $229.49   $229.50   $229.50  
  Purchase #6 $134.65   4.351%   $140.5086   $140.51   $140.50   $140.50  
  Purchase #7 $68.98   11.285%   $76.7644   $76.76   $76.75   $76.80  
  7 purchase totals = $958.64       $1,060.4601   $1,060.45   $1,060.45   $1,060.50