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 $70.36   12.649%   $79.2598   $79.26   $79.25   $79.30  
  Purchase #2 $240.80   4.392%   $251.3759   $251.38   $251.40   $251.40  
  Purchase #3 $159.75   5.767%   $168.9628   $168.96   $168.95   $169.00  
  Purchase #4 $153.53   9.295%   $167.8006   $167.80   $167.80   $167.80  
  Purchase #5 $23.54   7.272%   $25.2518   $25.25   $25.25   $25.30  
  Purchase #6 $172.48   11.662%   $192.5946   $192.59   $192.60   $192.60  
  Purchase #7 $151.46   6.632%   $161.5048   $161.50   $161.50   $161.50  
  7 purchase totals = $971.92       $1,046.7503   $1,046.74   $1,046.75   $1,046.90