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 $162.49   6.655%   $173.3037   $173.30   $173.30   $173.30  
  Purchase #2 $208.38   13.248%   $235.9862   $235.99   $236.00   $236.00  
  Purchase #3 $111.80   7.250%   $119.9055   $119.91   $119.90   $119.90  
  Purchase #4 $243.36   4.532%   $254.3891   $254.39   $254.40   $254.40  
  Purchase #5 $51.54   8.840%   $56.0961   $56.10   $56.10   $56.10  
  Purchase #6 $62.52   8.602%   $67.898   $67.90   $67.90   $67.90  
  Purchase #7 $64.90   6.286%   $68.9796   $68.98   $69.00   $69.00  
  7 purchase totals = $904.99       $976.5582   $976.57   $976.60   $976.60