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 $103.52   13.503%   $117.4983   $117.50   $117.50   $117.50  
  Purchase #2 $169.94   8.407%   $184.2269   $184.23   $184.25   $184.20  
  Purchase #3 $157.82   3.535%   $163.3989   $163.40   $163.40   $163.40  
  Purchase #4 $31.47   13.528%   $35.7273   $35.73   $35.75   $35.70  
  Purchase #5 $128.66   8.317%   $139.3607   $139.36   $139.35   $139.40  
  Purchase #6 $190.36   5.422%   $200.6813   $200.68   $200.70   $200.70  
  Purchase #7 $189.43   9.160%   $206.7818   $206.78   $206.80   $206.80  
  7 purchase totals = $971.20       $1,047.6752   $1,047.68   $1,047.75   $1,047.70