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 $136.41   5.580%   $144.0217   $144.02   $144.00   $144.00  
  Purchase #2 $218.27   3.547%   $226.012   $226.01   $226.00   $226.00  
  Purchase #3 $205.77   6.124%   $218.3714   $218.37   $218.35   $218.40  
  Purchase #4 $227.33   8.808%   $247.3532   $247.35   $247.35   $247.40  
  Purchase #5 $119.93   10.356%   $132.35   $132.35   $132.35   $132.40  
  Purchase #6 $132.46   10.660%   $146.5802   $146.58   $146.60   $146.60  
  Purchase #7 $53.83   10.810%   $59.649   $59.65   $59.65   $59.60  
  7 purchase totals = $1,094.00       $1,174.3375   $1,174.33   $1,174.30   $1,174.40