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 $67.90   11.569%   $75.7554   $75.76   $75.75   $75.80  
  Purchase #2 $116.53   13.617%   $132.3979   $132.40   $132.40   $132.40  
  Purchase #3 $168.36   9.620%   $184.5562   $184.56   $184.55   $184.60  
  Purchase #4 $244.48   12.634%   $275.3676   $275.37   $275.35   $275.40  
  Purchase #5 $168.54   8.627%   $183.0799   $183.08   $183.10   $183.10  
  Purchase #6 $225.87   11.323%   $251.4453   $251.45   $251.45   $251.40  
  Purchase #7 $144.84   9.748%   $158.959   $158.96   $158.95   $159.00  
  7 purchase totals = $1,136.52       $1,261.5613   $1,261.58   $1,261.55   $1,261.70