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 $77.25   5.571%   $81.5536   $81.55   $81.55   $81.60  
  Purchase #2 $194.58   5.790%   $205.8462   $205.85   $205.85   $205.80  
  Purchase #3 $205.76   7.597%   $221.3916   $221.39   $221.40   $221.40  
  Purchase #4 $28.62   5.238%   $30.1191   $30.12   $30.10   $30.10  
  Purchase #5 $103.63   13.427%   $117.5444   $117.54   $117.55   $117.50  
  Purchase #6 $21.38   12.787%   $24.1139   $24.11   $24.10   $24.10  
  Purchase #7 $123.50   10.200%   $136.097   $136.10   $136.10   $136.10  
  7 purchase totals = $754.72       $816.6658   $816.66   $816.65   $816.60