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 $197.86   12.151%   $221.902   $221.90   $221.90   $221.90  
  Purchase #2 $227.44   7.714%   $244.9847   $244.98   $245.00   $245.00  
  Purchase #3 $221.58   12.373%   $248.9961   $249.00   $249.00   $249.00  
  Purchase #4 $233.42   4.437%   $243.7768   $243.78   $243.80   $243.80  
  Purchase #5 $58.62   9.728%   $64.3226   $64.32   $64.30   $64.30  
  Purchase #6 $192.97   13.500%   $219.021   $219.02   $219.00   $219.00  
  Purchase #7 $63.32   4.739%   $66.3207   $66.32   $66.30   $66.30  
  7 purchase totals = $1,195.21       $1,309.3239   $1,309.32   $1,309.30   $1,309.30