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 $137.86   4.396%   $143.9203   $143.92   $143.90   $143.90  
  Purchase #2 $33.29   11.270%   $37.0418   $37.04   $37.05   $37.00  
  Purchase #3 $132.63   5.315%   $139.6793   $139.68   $139.70   $139.70  
  Purchase #4 $133.79   4.348%   $139.6072   $139.61   $139.60   $139.60  
  Purchase #5 $109.78   9.644%   $120.3672   $120.37   $120.35   $120.40  
  Purchase #6 $190.73   7.800%   $205.6069   $205.61   $205.60   $205.60  
  Purchase #7 $246.35   8.849%   $268.1495   $268.15   $268.15   $268.10  
  7 purchase totals = $984.43       $1,054.3722   $1,054.38   $1,054.35   $1,054.30