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 $24.66   4.853%   $25.8567   $25.86   $25.85   $25.90  
  Purchase #2 $182.65   11.447%   $203.5579   $203.56   $203.55   $203.60  
  Purchase #3 $196.66   13.412%   $223.036   $223.04   $223.05   $223.00  
  Purchase #4 $136.57   13.636%   $155.1927   $155.19   $155.20   $155.20  
  Purchase #5 $21.47   4.673%   $22.4733   $22.47   $22.45   $22.50  
  Purchase #6 $96.29   11.536%   $107.398   $107.40   $107.40   $107.40  
  Purchase #7 $39.77   9.511%   $43.5525   $43.55   $43.55   $43.60  
  7 purchase totals = $698.07       $781.0671   $781.07   $781.05   $781.20