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 $189.63   6.498%   $201.9522   $201.95   $201.95   $202.00  
  Purchase #2 $216.48   10.712%   $239.6693   $239.67   $239.65   $239.70  
  Purchase #3 $210.33   11.247%   $233.9858   $233.99   $234.00   $234.00  
  Purchase #4 $159.55   10.476%   $176.2645   $176.26   $176.25   $176.30  
  Purchase #5 $206.45   11.744%   $230.6955   $230.70   $230.70   $230.70  
  Purchase #6 $67.49   11.422%   $75.1987   $75.20   $75.20   $75.20  
  Purchase #7 $19.76   5.350%   $20.8172   $20.82   $20.80   $20.80  
  7 purchase totals = $1,069.69       $1,178.5832   $1,178.59   $1,178.55   $1,178.70