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 $244.83   11.237%   $272.3415   $272.34   $272.35   $272.30  
  Purchase #2 $229.97   10.583%   $254.3077   $254.31   $254.30   $254.30  
  Purchase #3 $166.97   5.453%   $176.0749   $176.07   $176.05   $176.10  
  Purchase #4 $75.90   7.426%   $81.5363   $81.54   $81.55   $81.50  
  Purchase #5 $99.44   13.732%   $113.0951   $113.10   $113.10   $113.10  
  Purchase #6 $59.50   9.365%   $65.0722   $65.07   $65.05   $65.10  
  Purchase #7 $138.95   4.295%   $144.9179   $144.92   $144.90   $144.90  
  7 purchase totals = $1,015.56       $1,107.3456   $1,107.35   $1,107.30   $1,107.30