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 $222.30   13.824%   $253.0308   $253.03   $253.05   $253.00  
  Purchase #2 $91.81   10.412%   $101.3693   $101.37   $101.35   $101.40  
  Purchase #3 $201.86   12.257%   $226.602   $226.60   $226.60   $226.60  
  Purchase #4 $67.85   7.225%   $72.7522   $72.75   $72.75   $72.80  
  Purchase #5 $77.84   4.834%   $81.6028   $81.60   $81.60   $81.60  
  Purchase #6 $159.70   12.238%   $179.2441   $179.24   $179.25   $179.20  
  Purchase #7 $245.33   10.612%   $271.3644   $271.36   $271.35   $271.40  
  7 purchase totals = $1,066.69       $1,185.9656   $1,185.95   $1,185.95   $1,186.00