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 $63.97   5.552%   $67.5216   $67.52   $67.50   $67.50  
  Purchase #2 $95.32   8.525%   $103.446   $103.45   $103.45   $103.40  
  Purchase #3 $96.44   5.669%   $101.9072   $101.91   $101.90   $101.90  
  Purchase #4 $67.41   13.837%   $76.7375   $76.74   $76.75   $76.70  
  Purchase #5 $113.48   7.829%   $122.3643   $122.36   $122.35   $122.40  
  Purchase #6 $186.33   10.371%   $205.6543   $205.65   $205.65   $205.70  
  Purchase #7 $202.99   7.339%   $217.8874   $217.89   $217.90   $217.90  
  7 purchase totals = $825.94       $895.5183   $895.52   $895.50   $895.50