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 $188.49   8.744%   $204.9716   $204.97   $204.95   $205.00  
  Purchase #2 $162.60   8.181%   $175.9023   $175.90   $175.90   $175.90  
  Purchase #3 $211.81   8.273%   $229.333   $229.33   $229.35   $229.30  
  Purchase #4 $126.75   8.334%   $137.3133   $137.31   $137.30   $137.30  
  Purchase #5 $116.99   13.272%   $132.5169   $132.52   $132.50   $132.50  
  Purchase #6 $66.89   9.781%   $73.4325   $73.43   $73.45   $73.40  
  Purchase #7 $84.68   9.115%   $92.3986   $92.40   $92.40   $92.40  
  7 purchase totals = $958.21       $1,045.8682   $1,045.86   $1,045.85   $1,045.80