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 $82.66   10.862%   $91.6385   $91.64   $91.65   $91.60  
  Purchase #2 $75.77   5.283%   $79.7729   $79.77   $79.75   $79.80  
  Purchase #3 $90.77   4.175%   $94.5596   $94.56   $94.55   $94.60  
  Purchase #4 $114.52   5.478%   $120.7934   $120.79   $120.80   $120.80  
  Purchase #5 $111.92   11.356%   $124.6296   $124.63   $124.65   $124.60  
  Purchase #6 $148.89   11.204%   $165.5716   $165.57   $165.55   $165.60  
  Purchase #7 $109.37   6.303%   $116.2636   $116.26   $116.25   $116.30  
  7 purchase totals = $733.90       $793.2292   $793.22   $793.20   $793.30