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 $108.67   10.119%   $119.6663   $119.67   $119.65   $119.70  
  Purchase #2 $171.52   7.137%   $183.7614   $183.76   $183.75   $183.80  
  Purchase #3 $114.70   13.261%   $129.9104   $129.91   $129.90   $129.90  
  Purchase #4 $243.93   4.246%   $254.2873   $254.29   $254.30   $254.30  
  Purchase #5 $94.46   6.337%   $100.4459   $100.45   $100.45   $100.40  
  Purchase #6 $5.60   10.274%   $6.1753   $6.18   $6.20   $6.20  
  Purchase #7 $167.92   4.643%   $175.7165   $175.72   $175.70   $175.70  
  7 purchase totals = $906.80       $969.9631   $969.98   $969.95   $970.00