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 $118.27   11.229%   $131.5505   $131.55   $131.55   $131.60  
  Purchase #2 $231.75   5.432%   $244.3387   $244.34   $244.35   $244.30  
  Purchase #3 $19.76   8.254%   $21.391   $21.39   $21.40   $21.40  
  Purchase #4 $216.54   8.246%   $234.3959   $234.40   $234.40   $234.40  
  Purchase #5 $143.60   3.536%   $148.6777   $148.68   $148.70   $148.70  
  Purchase #6 $231.25   4.387%   $241.3949   $241.39   $241.40   $241.40  
  Purchase #7 $210.52   5.741%   $222.606   $222.61   $222.60   $222.60  
  7 purchase totals = $1,171.69       $1,244.3547   $1,244.36   $1,244.40   $1,244.40