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 $220.98   5.111%   $232.2743   $232.27   $232.25   $232.30  
  Purchase #2 $108.69   9.818%   $119.3612   $119.36   $119.35   $119.40  
  Purchase #3 $202.96   11.612%   $226.5277   $226.53   $226.55   $226.50  
  Purchase #4 $122.28   4.584%   $127.8853   $127.89   $127.90   $127.90  
  Purchase #5 $78.36   6.786%   $83.6775   $83.68   $83.70   $83.70  
  Purchase #6 $13.76   12.498%   $15.4797   $15.48   $15.50   $15.50  
  Purchase #7 $239.43   3.437%   $247.6592   $247.66   $247.65   $247.70  
  7 purchase totals = $986.46       $1,052.8649   $1,052.87   $1,052.90   $1,053.00