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 $116.53   13.688%   $132.4806   $132.48   $132.50   $132.50  
  Purchase #2 $240.88   6.816%   $257.2984   $257.30   $257.30   $257.30  
  Purchase #3 $115.47   3.368%   $119.359   $119.36   $119.35   $119.40  
  Purchase #4 $219.92   7.111%   $235.5585   $235.56   $235.55   $235.60  
  Purchase #5 $250.51   13.223%   $283.6349   $283.63   $283.65   $283.60  
  Purchase #6 $145.53   12.173%   $163.2454   $163.25   $163.25   $163.20  
  Purchase #7 $206.37   8.865%   $224.6647   $224.66   $224.65   $224.70  
  7 purchase totals = $1,295.21       $1,416.2415   $1,416.24   $1,416.25   $1,416.30