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 $236.93   12.806%   $267.2713   $267.27   $267.25   $267.30  
  Purchase #2 $170.76   7.463%   $183.5038   $183.50   $183.50   $183.50  
  Purchase #3 $183.36   6.190%   $194.71   $194.71   $194.70   $194.70  
  Purchase #4 $37.75   8.124%   $40.8168   $40.82   $40.80   $40.80  
  Purchase #5 $35.31   9.202%   $38.5592   $38.56   $38.55   $38.60  
  Purchase #6 $138.60   12.786%   $156.3214   $156.32   $156.30   $156.30  
  Purchase #7 $109.77   11.843%   $122.7701   $122.77   $122.75   $122.80  
  7 purchase totals = $912.48       $1,003.9526   $1,003.95   $1,003.85   $1,004.00