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 $222.44   11.462%   $247.9361   $247.94   $247.95   $247.90  
  Purchase #2 $233.91   5.581%   $246.9645   $246.96   $246.95   $247.00  
  Purchase #3 $215.95   4.243%   $225.1128   $225.11   $225.10   $225.10  
  Purchase #4 $43.72   12.374%   $49.1299   $49.13   $49.15   $49.10  
  Purchase #5 $186.71   4.687%   $195.4611   $195.46   $195.45   $195.50  
  Purchase #6 $96.53   11.671%   $107.796   $107.80   $107.80   $107.80  
  Purchase #7 $82.66   11.145%   $91.8725   $91.87   $91.85   $91.90  
  7 purchase totals = $1,081.92       $1,164.2729   $1,164.27   $1,164.25   $1,164.30