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 $171.51   7.230%   $183.9102   $183.91   $183.90   $183.90  
  Purchase #2 $166.92   10.809%   $184.9624   $184.96   $184.95   $185.00  
  Purchase #3 $157.80   7.628%   $169.837   $169.84   $169.85   $169.80  
  Purchase #4 $38.64   5.285%   $40.6821   $40.68   $40.70   $40.70  
  Purchase #5 $122.38   3.199%   $126.2949   $126.29   $126.30   $126.30  
  Purchase #6 $167.85   3.549%   $173.807   $173.81   $173.80   $173.80  
  Purchase #7 $135.93   13.279%   $153.9801   $153.98   $154.00   $154.00  
  7 purchase totals = $961.03       $1,033.4737   $1,033.47   $1,033.50   $1,033.50