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 $61.57   7.175%   $65.9876   $65.99   $66.00   $66.00  
  Purchase #2 $138.94   10.453%   $153.4634   $153.46   $153.45   $153.50  
  Purchase #3 $49.48   7.832%   $53.3553   $53.36   $53.35   $53.40  
  Purchase #4 $135.71   6.764%   $144.8894   $144.89   $144.90   $144.90  
  Purchase #5 $68.34   9.148%   $74.5917   $74.59   $74.60   $74.60  
  Purchase #6 $246.93   5.564%   $260.6692   $260.67   $260.65   $260.70  
  Purchase #7 $47.72   3.808%   $49.5372   $49.54   $49.55   $49.50  
  7 purchase totals = $748.69       $802.4938   $802.50   $802.50   $802.60