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 $188.67   8.284%   $204.2994   $204.30   $204.30   $204.30  
  Purchase #2 $66.65   10.451%   $73.6156   $73.62   $73.60   $73.60  
  Purchase #3 $195.89   5.564%   $206.7893   $206.79   $206.80   $206.80  
  Purchase #4 $47.72   13.840%   $54.3244   $54.32   $54.30   $54.30  
  Purchase #5 $181.37   7.429%   $194.844   $194.84   $194.85   $194.80  
  Purchase #6 $137.45   7.872%   $148.2701   $148.27   $148.25   $148.30  
  Purchase #7 $199.67   7.867%   $215.378   $215.38   $215.40   $215.40  
  7 purchase totals = $1,017.42       $1,097.5208   $1,097.52   $1,097.50   $1,097.50