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 $189.57   7.448%   $203.6892   $203.69   $203.70   $203.70  
  Purchase #2 $58.98   6.815%   $62.9995   $63.00   $63.00   $63.00  
  Purchase #3 $15.61   9.257%   $17.055   $17.06   $17.05   $17.10  
  Purchase #4 $94.82   6.241%   $100.7377   $100.74   $100.75   $100.70  
  Purchase #5 $160.90   7.865%   $173.5548   $173.55   $173.55   $173.60  
  Purchase #6 $44.76   8.208%   $48.4339   $48.43   $48.45   $48.40  
  Purchase #7 $186.63   8.439%   $202.3797   $202.38   $202.40   $202.40  
  7 purchase totals = $751.27       $808.8498   $808.85   $808.90   $808.90