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 $217.58   6.453%   $231.6204   $231.62   $231.60   $231.60  
  Purchase #2 $196.79   7.555%   $211.6575   $211.66   $211.65   $211.70  
  Purchase #3 $104.40   5.742%   $110.3946   $110.39   $110.40   $110.40  
  Purchase #4 $247.77   11.162%   $275.4261   $275.43   $275.45   $275.40  
  Purchase #5 $9.32   12.400%   $10.4757   $10.48   $10.50   $10.50  
  Purchase #6 $176.34   12.197%   $197.8482   $197.85   $197.85   $197.80  
  Purchase #7 $181.64   3.767%   $188.4824   $188.48   $188.50   $188.50  
  7 purchase totals = $1,133.84       $1,225.9049   $1,225.91   $1,225.95   $1,225.90