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 $203.49   11.859%   $227.6219   $227.62   $227.60   $227.60  
  Purchase #2 $228.79   10.336%   $252.4377   $252.44   $252.45   $252.40  
  Purchase #3 $197.84   6.443%   $210.5868   $210.59   $210.60   $210.60  
  Purchase #4 $192.57   7.680%   $207.3594   $207.36   $207.35   $207.40  
  Purchase #5 $186.54   4.610%   $195.1395   $195.14   $195.15   $195.10  
  Purchase #6 $75.25   11.600%   $83.979   $83.98   $84.00   $84.00  
  Purchase #7 $189.83   6.532%   $202.2297   $202.23   $202.25   $202.20  
  7 purchase totals = $1,274.31       $1,379.3540   $1,379.36   $1,379.40   $1,379.30