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 $204.55   4.645%   $214.0513   $214.05   $214.05   $214.10  
  Purchase #2 $58.61   3.822%   $60.8501   $60.85   $60.85   $60.90  
  Purchase #3 $76.46   9.323%   $83.5884   $83.59   $83.60   $83.60  
  Purchase #4 $96.98   11.306%   $107.9446   $107.94   $107.95   $107.90  
  Purchase #5 $98.70   7.227%   $105.833   $105.83   $105.85   $105.80  
  Purchase #6 $114.95   5.356%   $121.1067   $121.11   $121.10   $121.10  
  Purchase #7 $85.62   4.757%   $89.6929   $89.69   $89.70   $89.70  
  7 purchase totals = $735.87       $783.0670   $783.06   $783.10   $783.10