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 $225.57   7.277%   $241.9847   $241.98   $242.00   $242.00  
  Purchase #2 $136.37   3.541%   $141.1989   $141.20   $141.20   $141.20  
  Purchase #3 $162.46   12.106%   $182.1274   $182.13   $182.15   $182.10  
  Purchase #4 $250.85   4.671%   $262.5672   $262.57   $262.55   $262.60  
  Purchase #5 $26.50   10.492%   $29.2804   $29.28   $29.30   $29.30  
  Purchase #6 $113.35   3.283%   $117.0713   $117.07   $117.05   $117.10  
  Purchase #7 $33.79   12.584%   $38.0421   $38.04   $38.05   $38.00  
  7 purchase totals = $948.89       $1,012.2720   $1,012.27   $1,012.30   $1,012.30