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 $207.49   13.868%   $236.2647   $236.26   $236.25   $236.30  
  Purchase #2 $227.32   10.348%   $250.8431   $250.84   $250.85   $250.80  
  Purchase #3 $247.59   9.698%   $271.6013   $271.60   $271.60   $271.60  
  Purchase #4 $55.67   3.612%   $57.6808   $57.68   $57.70   $57.70  
  Purchase #5 $191.98   10.725%   $212.5699   $212.57   $212.55   $212.60  
  Purchase #6 $234.51   6.676%   $250.1659   $250.17   $250.15   $250.20  
  Purchase #7 $175.92   7.556%   $189.2125   $189.21   $189.20   $189.20  
  7 purchase totals = $1,340.48       $1,468.3382   $1,468.33   $1,468.30   $1,468.40