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 $58.67   8.534%   $63.6769   $63.68   $63.70   $63.70  
  Purchase #2 $167.95   12.435%   $188.8346   $188.83   $188.85   $188.80  
  Purchase #3 $61.82   12.543%   $69.5741   $69.57   $69.55   $69.60  
  Purchase #4 $46.84   12.566%   $52.7259   $52.73   $52.75   $52.70  
  Purchase #5 $193.45   4.736%   $202.6118   $202.61   $202.60   $202.60  
  Purchase #6 $183.57   7.798%   $197.8848   $197.88   $197.90   $197.90  
  Purchase #7 $142.68   13.145%   $161.4353   $161.44   $161.45   $161.40  
  7 purchase totals = $854.98       $936.7434   $936.74   $936.80   $936.70