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 $246.91   7.323%   $264.9912   $264.99   $265.00   $265.00  
  Purchase #2 $210.58   3.197%   $217.3122   $217.31   $217.30   $217.30  
  Purchase #3 $234.78   9.122%   $256.1966   $256.20   $256.20   $256.20  
  Purchase #4 $174.95   10.556%   $193.4177   $193.42   $193.40   $193.40  
  Purchase #5 $79.29   6.584%   $84.5105   $84.51   $84.50   $84.50  
  Purchase #6 $219.48   5.215%   $230.9259   $230.93   $230.95   $230.90  
  Purchase #7 $191.74   6.493%   $204.1897   $204.19   $204.20   $204.20  
  7 purchase totals = $1,357.73       $1,451.5438   $1,451.55   $1,451.55   $1,451.50