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 $184.71   12.369%   $207.5568   $207.56   $207.55   $207.60  
  Purchase #2 $90.88   6.123%   $96.4446   $96.44   $96.45   $96.40  
  Purchase #3 $211.49   4.184%   $220.3387   $220.34   $220.35   $220.30  
  Purchase #4 $148.77   3.652%   $154.2031   $154.20   $154.20   $154.20  
  Purchase #5 $96.31   8.787%   $104.7728   $104.77   $104.75   $104.80  
  Purchase #6 $46.45   4.109%   $48.3586   $48.36   $48.35   $48.40  
  Purchase #7 $231.72   5.525%   $244.5225   $244.52   $244.50   $244.50  
  7 purchase totals = $1,010.33       $1,076.1971   $1,076.19   $1,076.15   $1,076.20