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 $93.84   4.726%   $98.2749   $98.27   $98.25   $98.30  
  Purchase #2 $59.94   11.276%   $66.6988   $66.70   $66.70   $66.70  
  Purchase #3 $127.33   5.631%   $134.5   $134.50   $134.50   $134.50  
  Purchase #4 $192.49   9.424%   $210.6303   $210.63   $210.65   $210.60  
  Purchase #5 $139.39   4.304%   $145.3893   $145.39   $145.40   $145.40  
  Purchase #6 $61.28   9.604%   $67.1653   $67.17   $67.15   $67.20  
  Purchase #7 $219.26   10.205%   $241.6355   $241.64   $241.65   $241.60  
  7 purchase totals = $893.53       $964.2941   $964.30   $964.30   $964.30