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 $244.50   9.453%   $267.6126   $267.61   $267.60   $267.60  
  Purchase #2 $227.72   5.496%   $240.2355   $240.24   $240.25   $240.20  
  Purchase #3 $241.68   7.374%   $259.5015   $259.50   $259.50   $259.50  
  Purchase #4 $151.97   13.795%   $172.9343   $172.93   $172.95   $172.90  
  Purchase #5 $232.69   5.338%   $245.111   $245.11   $245.10   $245.10  
  Purchase #6 $102.60   7.756%   $110.5577   $110.56   $110.55   $110.60  
  Purchase #7 $56.37   11.815%   $63.0301   $63.03   $63.05   $63.00  
  7 purchase totals = $1,257.53       $1,358.9827   $1,358.98   $1,359.00   $1,358.90