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 $202.62   8.357%   $219.553   $219.55   $219.55   $219.60  
  Purchase #2 $128.94   13.265%   $146.0439   $146.04   $146.05   $146.00  
  Purchase #3 $19.51   10.673%   $21.5923   $21.59   $21.60   $21.60  
  Purchase #4 $213.69   13.180%   $241.8543   $241.85   $241.85   $241.90  
  Purchase #5 $170.91   3.371%   $176.6714   $176.67   $176.65   $176.70  
  Purchase #6 $149.36   3.487%   $154.5682   $154.57   $154.55   $154.60  
  Purchase #7 $60.61   4.465%   $63.3162   $63.32   $63.30   $63.30  
  7 purchase totals = $945.64       $1,023.5993   $1,023.59   $1,023.55   $1,023.70