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 $62.34   9.678%   $68.3733   $68.37   $68.35   $68.40  
  Purchase #2 $214.42   5.649%   $226.5326   $226.53   $226.55   $226.50  
  Purchase #3 $127.74   8.177%   $138.1853   $138.19   $138.20   $138.20  
  Purchase #4 $7.97   13.430%   $9.0404   $9.04   $9.05   $9.00  
  Purchase #5 $201.37   11.786%   $225.1035   $225.10   $225.10   $225.10  
  Purchase #6 $84.79   9.592%   $92.9231   $92.92   $92.90   $92.90  
  Purchase #7 $61.51   10.182%   $67.7729   $67.77   $67.75   $67.80  
  7 purchase totals = $760.14       $827.9311   $827.92   $827.90   $827.90