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 $44.83   7.246%   $48.0784   $48.08   $48.10   $48.10  
  Purchase #2 $145.83   4.688%   $152.6665   $152.67   $152.65   $152.70  
  Purchase #3 $154.69   3.383%   $159.9232   $159.92   $159.90   $159.90  
  Purchase #4 $64.82   13.507%   $73.5752   $73.58   $73.60   $73.60  
  Purchase #5 $130.78   12.182%   $146.7116   $146.71   $146.70   $146.70  
  Purchase #6 $142.71   3.201%   $147.2781   $147.28   $147.30   $147.30  
  Purchase #7 $218.37   10.418%   $241.1198   $241.12   $241.10   $241.10  
  7 purchase totals = $902.03       $969.3528   $969.36   $969.35   $969.40