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 $119.65   7.233%   $128.3043   $128.30   $128.30   $128.30  
  Purchase #2 $67.80   4.601%   $70.9195   $70.92   $70.90   $70.90  
  Purchase #3 $94.63   6.471%   $100.7535   $100.75   $100.75   $100.80  
  Purchase #4 $59.98   11.229%   $66.7152   $66.72   $66.70   $66.70  
  Purchase #5 $93.31   5.643%   $98.5755   $98.58   $98.60   $98.60  
  Purchase #6 $183.59   5.816%   $194.2676   $194.27   $194.25   $194.30  
  Purchase #7 $241.99   7.174%   $259.3504   $259.35   $259.35   $259.40  
  7 purchase totals = $860.95       $918.8860   $918.89   $918.85   $919.00