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 $88.78   4.716%   $92.9669   $92.97   $92.95   $93.00  
  Purchase #2 $79.86   11.150%   $88.7644   $88.76   $88.75   $88.80  
  Purchase #3 $113.29   13.468%   $128.5479   $128.55   $128.55   $128.50  
  Purchase #4 $243.74   9.122%   $265.974   $265.97   $265.95   $266.00  
  Purchase #5 $243.62   8.255%   $263.7308   $263.73   $263.75   $263.70  
  Purchase #6 $235.99   6.719%   $251.8462   $251.85   $251.85   $251.80  
  Purchase #7 $119.63   5.518%   $126.2312   $126.23   $126.25   $126.20  
  7 purchase totals = $1,124.91       $1,218.0614   $1,218.06   $1,218.05   $1,218.00