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 $39.84   11.823%   $44.5503   $44.55   $44.55   $44.60  
  Purchase #2 $98.48   12.313%   $110.6058   $110.61   $110.60   $110.60  
  Purchase #3 $180.43   13.510%   $204.8061   $204.81   $204.80   $204.80  
  Purchase #4 $217.25   11.256%   $241.7037   $241.70   $241.70   $241.70  
  Purchase #5 $169.45   5.199%   $178.2597   $178.26   $178.25   $178.30  
  Purchase #6 $136.28   6.150%   $144.6612   $144.66   $144.65   $144.70  
  Purchase #7 $138.50   9.763%   $152.0218   $152.02   $152.00   $152.00  
  7 purchase totals = $980.23       $1,076.6086   $1,076.61   $1,076.55   $1,076.70