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 $241.80   7.223%   $259.2652   $259.27   $259.25   $259.30  
  Purchase #2 $184.50   4.769%   $193.2988   $193.30   $193.30   $193.30  
  Purchase #3 $211.62   12.834%   $238.7793   $238.78   $238.80   $238.80  
  Purchase #4 $118.33   5.846%   $125.2476   $125.25   $125.25   $125.20  
  Purchase #5 $209.92   9.847%   $230.5908   $230.59   $230.60   $230.60  
  Purchase #6 $112.96   13.300%   $127.9837   $127.98   $128.00   $128.00  
  Purchase #7 $112.76   13.159%   $127.5981   $127.60   $127.60   $127.60  
  7 purchase totals = $1,191.89       $1,302.7635   $1,302.77   $1,302.80   $1,302.80