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 $238.71   11.706%   $266.6534   $266.65   $266.65   $266.70  
  Purchase #2 $89.66   7.699%   $96.5629   $96.56   $96.55   $96.60  
  Purchase #3 $117.38   6.519%   $125.032   $125.03   $125.05   $125.00  
  Purchase #4 $204.78   8.412%   $222.0061   $222.01   $222.00   $222.00  
  Purchase #5 $94.40   10.715%   $104.515   $104.52   $104.50   $104.50  
  Purchase #6 $26.25   9.460%   $28.7333   $28.73   $28.75   $28.70  
  Purchase #7 $243.29   12.715%   $274.2243   $274.22   $274.20   $274.20  
  7 purchase totals = $1,014.47       $1,117.7270   $1,117.72   $1,117.70   $1,117.70