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 $70.58   4.109%   $73.4801   $73.48   $73.50   $73.50  
  Purchase #2 $238.65   11.312%   $265.6461   $265.65   $265.65   $265.60  
  Purchase #3 $154.62   10.301%   $170.5474   $170.55   $170.55   $170.50  
  Purchase #4 $81.68   8.377%   $88.5223   $88.52   $88.50   $88.50  
  Purchase #5 $154.57   8.207%   $167.2556   $167.26   $167.25   $167.30  
  Purchase #6 $152.69   9.116%   $166.6092   $166.61   $166.60   $166.60  
  Purchase #7 $46.84   5.659%   $49.4907   $49.49   $49.50   $49.50  
  7 purchase totals = $899.63       $981.5514   $981.56   $981.55   $981.50