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 $62.28   6.257%   $66.1769   $66.18   $66.20   $66.20  
  Purchase #2 $158.32   11.122%   $175.9284   $175.93   $175.95   $175.90  
  Purchase #3 $233.26   11.213%   $259.4154   $259.42   $259.40   $259.40  
  Purchase #4 $44.81   6.152%   $47.5667   $47.57   $47.55   $47.60  
  Purchase #5 $100.53   6.403%   $106.9669   $106.97   $106.95   $107.00  
  Purchase #6 $158.94   9.848%   $174.5924   $174.59   $174.60   $174.60  
  Purchase #7 $119.57   6.490%   $127.3301   $127.33   $127.35   $127.30  
  7 purchase totals = $877.71       $957.9768   $957.99   $958.00   $958.00