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 $246.78   11.691%   $275.631   $275.63   $275.65   $275.60  
  Purchase #2 $205.56   13.106%   $232.5007   $232.50   $232.50   $232.50  
  Purchase #3 $98.33   12.211%   $110.3371   $110.34   $110.35   $110.30  
  Purchase #4 $176.39   5.538%   $186.1585   $186.16   $186.15   $186.20  
  Purchase #5 $6.26   3.855%   $6.5013   $6.50   $6.50   $6.50  
  Purchase #6 $209.33   13.393%   $237.3656   $237.37   $237.35   $237.40  
  Purchase #7 $55.42   7.562%   $59.6109   $59.61   $59.60   $59.60  
  7 purchase totals = $998.07       $1,108.1051   $1,108.11   $1,108.10   $1,108.10