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 $218.49   10.312%   $241.0207   $241.02   $241.00   $241.00  
  Purchase #2 $195.87   12.489%   $220.3322   $220.33   $220.35   $220.30  
  Purchase #3 $36.71   3.629%   $38.0422   $38.04   $38.05   $38.00  
  Purchase #4 $44.85   4.268%   $46.7642   $46.76   $46.75   $46.80  
  Purchase #5 $204.63   11.104%   $227.3521   $227.35   $227.35   $227.40  
  Purchase #6 $245.44   10.151%   $270.3546   $270.35   $270.35   $270.40  
  Purchase #7 $129.37   4.663%   $135.4025   $135.40   $135.40   $135.40  
  7 purchase totals = $1,075.36       $1,179.2685   $1,179.25   $1,179.25   $1,179.30