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 $53.84   7.648%   $57.9577   $57.96   $57.95   $58.00  
  Purchase #2 $36.87   13.779%   $41.9503   $41.95   $41.95   $42.00  
  Purchase #3 $250.73   4.542%   $262.1182   $262.12   $262.10   $262.10  
  Purchase #4 $225.36   11.568%   $251.4296   $251.43   $251.45   $251.40  
  Purchase #5 $63.91   5.289%   $67.2902   $67.29   $67.30   $67.30  
  Purchase #6 $186.66   12.405%   $209.8152   $209.82   $209.80   $209.80  
  Purchase #7 $16.79   7.565%   $18.0602   $18.06   $18.05   $18.10  
  7 purchase totals = $834.16       $908.6214   $908.63   $908.60   $908.70