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 $183.26   7.852%   $197.6496   $197.65   $197.65   $197.60  
  Purchase #2 $240.84   4.593%   $251.9018   $251.90   $251.90   $251.90  
  Purchase #3 $243.50   10.645%   $269.4206   $269.42   $269.40   $269.40  
  Purchase #4 $33.87   3.406%   $35.0236   $35.02   $35.00   $35.00  
  Purchase #5 $100.77   13.548%   $114.4223   $114.42   $114.40   $114.40  
  Purchase #6 $236.52   10.820%   $262.1115   $262.11   $262.10   $262.10  
  Purchase #7 $239.64   4.577%   $250.6083   $250.61   $250.60   $250.60  
  7 purchase totals = $1,278.40       $1,381.1377   $1,381.13   $1,381.05   $1,381.00