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 $95.28   8.870%   $103.7313   $103.73   $103.75   $103.70  
  Purchase #2 $143.42   13.432%   $162.6842   $162.68   $162.70   $162.70  
  Purchase #3 $189.28   8.813%   $205.9612   $205.96   $205.95   $206.00  
  Purchase #4 $52.98   7.679%   $57.0483   $57.05   $57.05   $57.00  
  Purchase #5 $64.40   9.439%   $70.4787   $70.48   $70.50   $70.50  
  Purchase #6 $103.69   13.563%   $117.7535   $117.75   $117.75   $117.80  
  Purchase #7 $230.52   5.487%   $243.1686   $243.17   $243.15   $243.20  
  7 purchase totals = $879.57       $960.8258   $960.82   $960.85   $960.90