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 $117.52   8.789%   $127.8488   $127.85   $127.85   $127.80  
  Purchase #2 $146.62   4.727%   $153.5507   $153.55   $153.55   $153.60  
  Purchase #3 $88.85   5.769%   $93.9758   $93.98   $94.00   $94.00  
  Purchase #4 $208.92   13.608%   $237.3498   $237.35   $237.35   $237.30  
  Purchase #5 $69.28   13.669%   $78.7499   $78.75   $78.75   $78.70  
  Purchase #6 $115.91   10.396%   $127.96   $127.96   $127.95   $128.00  
  Purchase #7 $69.90   8.646%   $75.9436   $75.94   $75.95   $75.90  
  7 purchase totals = $817.00       $895.3786   $895.38   $895.40   $895.30