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 $181.25   10.870%   $200.9519   $200.95   $200.95   $201.00  
  Purchase #2 $32.36   9.631%   $35.4766   $35.48   $35.50   $35.50  
  Purchase #3 $119.94   3.592%   $124.2482   $124.25   $124.25   $124.20  
  Purchase #4 $128.64   11.721%   $143.7179   $143.72   $143.70   $143.70  
  Purchase #5 $133.86   4.812%   $140.3013   $140.30   $140.30   $140.30  
  Purchase #6 $225.85   4.864%   $236.8353   $236.84   $236.85   $236.80  
  Purchase #7 $199.32   5.236%   $209.7564   $209.76   $209.75   $209.80  
  7 purchase totals = $1,021.22       $1,091.2876   $1,091.30   $1,091.30   $1,091.30