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 $32.87   7.874%   $35.4582   $35.46   $35.45   $35.50  
  Purchase #2 $191.50   6.655%   $204.2443   $204.24   $204.25   $204.20  
  Purchase #3 $153.58   10.693%   $170.0023   $170.00   $170.00   $170.00  
  Purchase #4 $146.61   10.202%   $161.5672   $161.57   $161.55   $161.60  
  Purchase #5 $23.44   11.290%   $26.0864   $26.09   $26.10   $26.10  
  Purchase #6 $196.53   11.454%   $219.0405   $219.04   $219.05   $219.00  
  Purchase #7 $191.63   7.806%   $206.5886   $206.59   $206.60   $206.60  
  7 purchase totals = $936.16       $1,022.9875   $1,022.99   $1,023.00   $1,023.00