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 $55.84   11.378%   $62.1935   $62.19   $62.20   $62.20  
  Purchase #2 $16.31   6.346%   $17.345   $17.35   $17.35   $17.30  
  Purchase #3 $212.97   3.288%   $219.9725   $219.97   $219.95   $220.00  
  Purchase #4 $164.59   9.214%   $179.7553   $179.76   $179.75   $179.80  
  Purchase #5 $229.71   9.477%   $251.4796   $251.48   $251.50   $251.50  
  Purchase #6 $62.62   6.710%   $66.8218   $66.82   $66.80   $66.80  
  Purchase #7 $56.89   10.690%   $62.9715   $62.97   $62.95   $63.00  
  7 purchase totals = $798.93       $860.5392   $860.54   $860.50   $860.60