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 $41.94   3.504%   $43.4096   $43.41   $43.40   $43.40  
  Purchase #2 $158.42   3.837%   $164.4986   $164.50   $164.50   $164.50  
  Purchase #3 $247.96   13.572%   $281.6131   $281.61   $281.60   $281.60  
  Purchase #4 $105.85   11.419%   $117.937   $117.94   $117.95   $117.90  
  Purchase #5 $236.84   6.226%   $251.5857   $251.59   $251.60   $251.60  
  Purchase #6 $205.67   5.124%   $216.2085   $216.21   $216.20   $216.20  
  Purchase #7 $42.77   3.665%   $44.3375   $44.34   $44.35   $44.30  
  7 purchase totals = $1,039.45       $1,119.5900   $1,119.60   $1,119.60   $1,119.50