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 $244.37   3.534%   $253.006   $253.01   $253.00   $253.00  
  Purchase #2 $218.47   4.287%   $227.8358   $227.84   $227.85   $227.80  
  Purchase #3 $153.53   9.574%   $168.229   $168.23   $168.25   $168.20  
  Purchase #4 $66.26   6.494%   $70.5629   $70.56   $70.55   $70.60  
  Purchase #5 $144.66   12.324%   $162.4879   $162.49   $162.50   $162.50  
  Purchase #6 $167.51   13.518%   $190.154   $190.15   $190.15   $190.20  
  Purchase #7 $199.84   13.114%   $226.047   $226.05   $226.05   $226.00  
  7 purchase totals = $1,194.64       $1,298.3226   $1,298.33   $1,298.35   $1,298.30