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 $173.62   13.657%   $197.3313   $197.33   $197.35   $197.30  
  Purchase #2 $202.45   11.793%   $226.3249   $226.32   $226.30   $226.30  
  Purchase #3 $182.38   11.387%   $203.1476   $203.15   $203.15   $203.10  
  Purchase #4 $92.64   3.494%   $95.8768   $95.88   $95.90   $95.90  
  Purchase #5 $38.33   3.556%   $39.693   $39.69   $39.70   $39.70  
  Purchase #6 $163.59   11.709%   $182.7448   $182.74   $182.75   $182.70  
  Purchase #7 $17.87   6.351%   $19.0049   $19.00   $19.00   $19.00  
  7 purchase totals = $870.88       $964.1233   $964.11   $964.15   $964.00