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 $223.73   13.319%   $253.5286   $253.53   $253.55   $253.50  
  Purchase #2 $125.85   10.745%   $139.3726   $139.37   $139.35   $139.40  
  Purchase #3 $146.55   3.715%   $151.9943   $151.99   $152.00   $152.00  
  Purchase #4 $102.74   6.820%   $109.7469   $109.75   $109.75   $109.70  
  Purchase #5 $195.88   5.872%   $207.3821   $207.38   $207.40   $207.40  
  Purchase #6 $24.91   13.108%   $28.1752   $28.18   $28.20   $28.20  
  Purchase #7 $172.27   7.841%   $185.7777   $185.78   $185.80   $185.80  
  7 purchase totals = $991.93       $1,075.9774   $1,075.98   $1,076.05   $1,076.00