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 $188.99   12.122%   $211.8994   $211.90   $211.90   $211.90  
  Purchase #2 $197.71   13.718%   $224.8319   $224.83   $224.85   $224.80  
  Purchase #3 $61.32   9.355%   $67.0565   $67.06   $67.05   $67.10  
  Purchase #4 $244.35   8.741%   $265.7086   $265.71   $265.70   $265.70  
  Purchase #5 $163.39   6.871%   $174.6165   $174.62   $174.60   $174.60  
  Purchase #6 $78.70   8.499%   $85.3887   $85.39   $85.40   $85.40  
  Purchase #7 $214.59   9.627%   $235.2486   $235.25   $235.25   $235.20  
  7 purchase totals = $1,149.05       $1,264.7502   $1,264.76   $1,264.75   $1,264.70