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 $10.95   8.154%   $11.8429   $11.84   $11.85   $11.80  
  Purchase #2 $48.36   5.149%   $50.8501   $50.85   $50.85   $50.90  
  Purchase #3 $177.50   4.691%   $185.8265   $185.83   $185.85   $185.80  
  Purchase #4 $180.84   13.498%   $205.2498   $205.25   $205.25   $205.20  
  Purchase #5 $58.59   13.790%   $66.6696   $66.67   $66.65   $66.70  
  Purchase #6 $30.93   3.453%   $31.998   $32.00   $32.00   $32.00  
  Purchase #7 $233.28   6.783%   $249.1034   $249.10   $249.10   $249.10  
  7 purchase totals = $740.45       $801.5403   $801.54   $801.55   $801.50