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 $228.87   10.650%   $253.2447   $253.24   $253.25   $253.20  
  Purchase #2 $222.31   10.326%   $245.2657   $245.27   $245.25   $245.30  
  Purchase #3 $161.26   8.541%   $175.0332   $175.03   $175.05   $175.00  
  Purchase #4 $133.83   9.727%   $146.8476   $146.85   $146.85   $146.80  
  Purchase #5 $244.80   11.298%   $272.4575   $272.46   $272.45   $272.50  
  Purchase #6 $164.84   7.162%   $176.6458   $176.65   $176.65   $176.60  
  Purchase #7 $47.32   4.718%   $49.5526   $49.55   $49.55   $49.60  
  7 purchase totals = $1,203.23       $1,319.0471   $1,319.05   $1,319.05   $1,319.00