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 $247.94   12.801%   $279.6788   $279.68   $279.70   $279.70  
  Purchase #2 $87.73   9.374%   $95.9538   $95.95   $95.95   $96.00  
  Purchase #3 $224.87   9.422%   $246.0573   $246.06   $246.05   $246.10  
  Purchase #4 $30.55   11.855%   $34.1717   $34.17   $34.15   $34.20  
  Purchase #5 $202.49   13.492%   $229.81   $229.81   $229.80   $229.80  
  Purchase #6 $214.34   8.727%   $233.0455   $233.05   $233.05   $233.00  
  Purchase #7 $141.45   7.484%   $152.0361   $152.04   $152.05   $152.00  
  7 purchase totals = $1,149.37       $1,270.7532   $1,270.76   $1,270.75   $1,270.80