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 $219.57   11.870%   $245.633   $245.63   $245.65   $245.60  
  Purchase #2 $218.85   11.238%   $243.4444   $243.44   $243.45   $243.40  
  Purchase #3 $250.66   3.602%   $259.6888   $259.69   $259.70   $259.70  
  Purchase #4 $72.94   5.349%   $76.8416   $76.84   $76.85   $76.80  
  Purchase #5 $175.98   6.609%   $187.6105   $187.61   $187.60   $187.60  
  Purchase #6 $94.96   11.848%   $106.2109   $106.21   $106.20   $106.20  
  Purchase #7 $95.56   5.592%   $100.9037   $100.90   $100.90   $100.90  
  7 purchase totals = $1,128.52       $1,220.3329   $1,220.32   $1,220.35   $1,220.20