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 $62.83   5.412%   $66.2304   $66.23   $66.25   $66.20  
  Purchase #2 $242.51   11.281%   $269.8676   $269.87   $269.85   $269.90  
  Purchase #3 $17.66   10.668%   $19.544   $19.54   $19.55   $19.50  
  Purchase #4 $177.91   13.274%   $201.5258   $201.53   $201.55   $201.50  
  Purchase #5 $124.97   8.278%   $135.315   $135.32   $135.30   $135.30  
  Purchase #6 $134.56   6.463%   $143.2566   $143.26   $143.25   $143.30  
  Purchase #7 $88.77   3.733%   $92.0838   $92.08   $92.10   $92.10  
  7 purchase totals = $849.21       $927.8232   $927.83   $927.85   $927.80