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 $241.47   11.533%   $269.3187   $269.32   $269.30   $269.30  
  Purchase #2 $120.92   8.798%   $131.5585   $131.56   $131.55   $131.60  
  Purchase #3 $224.71   4.461%   $234.7343   $234.73   $234.75   $234.70  
  Purchase #4 $141.75   3.664%   $146.9437   $146.94   $146.95   $146.90  
  Purchase #5 $82.33   11.153%   $91.5123   $91.51   $91.50   $91.50  
  Purchase #6 $152.84   3.181%   $157.7018   $157.70   $157.70   $157.70  
  Purchase #7 $126.93   3.672%   $131.5909   $131.59   $131.60   $131.60  
  7 purchase totals = $1,090.95       $1,163.3602   $1,163.35   $1,163.35   $1,163.30