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 $54.72   7.695%   $58.9307   $58.93   $58.95   $58.90  
  Purchase #2 $226.87   9.106%   $247.5288   $247.53   $247.55   $247.50  
  Purchase #3 $26.82   11.360%   $29.8668   $29.87   $29.85   $29.90  
  Purchase #4 $202.75   3.550%   $209.9476   $209.95   $209.95   $209.90  
  Purchase #5 $220.70   5.169%   $232.108   $232.11   $232.10   $232.10  
  Purchase #6 $195.35   9.630%   $214.1622   $214.16   $214.15   $214.20  
  Purchase #7 $19.61   6.217%   $20.8292   $20.83   $20.85   $20.80  
  7 purchase totals = $946.82       $1,013.3733   $1,013.38   $1,013.40   $1,013.30