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 $58.84   6.646%   $62.7505   $62.75   $62.75   $62.80  
  Purchase #2 $221.95   8.745%   $241.3595   $241.36   $241.35   $241.40  
  Purchase #3 $156.60   5.388%   $165.0376   $165.04   $165.05   $165.00  
  Purchase #4 $137.56   13.204%   $155.7234   $155.72   $155.70   $155.70  
  Purchase #5 $112.59   11.453%   $125.4849   $125.48   $125.50   $125.50  
  Purchase #6 $20.77   13.467%   $23.5671   $23.57   $23.55   $23.60  
  Purchase #7 $33.50   8.715%   $36.4195   $36.42   $36.40   $36.40  
  7 purchase totals = $741.81       $810.3425   $810.34   $810.30   $810.40