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 $61.87   13.446%   $70.189   $70.19   $70.20   $70.20  
  Purchase #2 $131.86   6.639%   $140.6142   $140.61   $140.60   $140.60  
  Purchase #3 $168.66   12.182%   $189.2062   $189.21   $189.20   $189.20  
  Purchase #4 $241.93   8.845%   $263.3287   $263.33   $263.35   $263.30  
  Purchase #5 $197.29   7.269%   $211.631   $211.63   $211.65   $211.60  
  Purchase #6 $146.68   12.425%   $164.905   $164.91   $164.90   $164.90  
  Purchase #7 $200.51   3.805%   $208.1394   $208.14   $208.15   $208.10  
  7 purchase totals = $1,148.80       $1,248.0135   $1,248.02   $1,248.05   $1,247.90