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 $170.77   7.530%   $183.629   $183.63   $183.65   $183.60  
  Purchase #2 $75.64   3.823%   $78.5317   $78.53   $78.55   $78.50  
  Purchase #3 $62.80   5.560%   $66.2917   $66.29   $66.30   $66.30  
  Purchase #4 $177.37   4.817%   $185.9139   $185.91   $185.90   $185.90  
  Purchase #5 $164.67   10.500%   $181.9604   $181.96   $181.95   $182.00  
  Purchase #6 $106.94   12.303%   $120.0968   $120.10   $120.10   $120.10  
  Purchase #7 $114.87   4.549%   $120.0954   $120.10   $120.10   $120.10  
  7 purchase totals = $873.06       $936.5189   $936.52   $936.55   $936.50