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 $76.75   10.204%   $84.5816   $84.58   $84.60   $84.60  
  Purchase #2 $23.90   12.466%   $26.8794   $26.88   $26.90   $26.90  
  Purchase #3 $109.95   5.515%   $116.0137   $116.01   $116.00   $116.00  
  Purchase #4 $83.79   13.345%   $94.9718   $94.97   $94.95   $95.00  
  Purchase #5 $10.54   3.491%   $10.908   $10.91   $10.90   $10.90  
  Purchase #6 $49.29   9.258%   $53.8533   $53.85   $53.85   $53.90  
  Purchase #7 $118.99   13.824%   $135.4392   $135.44   $135.45   $135.40  
  7 purchase totals = $473.21       $522.6470   $522.64   $522.65   $522.70