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 $84.37   12.536%   $94.9466   $94.95   $94.95   $94.90  
  Purchase #2 $141.70   7.404%   $152.1915   $152.19   $152.20   $152.20  
  Purchase #3 $94.39   4.648%   $98.7772   $98.78   $98.80   $98.80  
  Purchase #4 $68.49   9.552%   $75.0322   $75.03   $75.05   $75.00  
  Purchase #5 $12.58   6.459%   $13.3925   $13.39   $13.40   $13.40  
  Purchase #6 $36.57   4.240%   $38.1206   $38.12   $38.10   $38.10  
  Purchase #7 $96.32   13.423%   $109.249   $109.25   $109.25   $109.20  
  7 purchase totals = $534.42       $581.7096   $581.71   $581.75   $581.60