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 $34.29   4.441%   $35.8128   $35.81   $35.80   $35.80  
  Purchase #2 $105.56   13.342%   $119.6438   $119.64   $119.65   $119.60  
  Purchase #3 $132.42   8.403%   $143.5473   $143.55   $143.55   $143.50  
  Purchase #4 $167.93   5.564%   $177.2736   $177.27   $177.25   $177.30  
  Purchase #5 $171.80   13.452%   $194.9105   $194.91   $194.90   $194.90  
  Purchase #6 $54.92   13.288%   $62.2178   $62.22   $62.20   $62.20  
  Purchase #7 $106.78   10.374%   $117.8574   $117.86   $117.85   $117.90  
  7 purchase totals = $773.70       $851.2632   $851.26   $851.20   $851.20