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 $216.53   13.739%   $246.2791   $246.28   $246.30   $246.30  
  Purchase #2 $179.38   7.393%   $192.6416   $192.64   $192.65   $192.60  
  Purchase #3 $29.95   13.537%   $34.0043   $34.00   $34.00   $34.00  
  Purchase #4 $221.86   3.376%   $229.35   $229.35   $229.35   $229.40  
  Purchase #5 $127.85   4.111%   $133.1059   $133.11   $133.10   $133.10  
  Purchase #6 $174.80   10.251%   $192.7187   $192.72   $192.70   $192.70  
  Purchase #7 $158.35   7.532%   $170.2769   $170.28   $170.30   $170.30  
  7 purchase totals = $1,108.72       $1,198.3765   $1,198.38   $1,198.40   $1,198.40