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 $114.39   7.694%   $123.1912   $123.19   $123.20   $123.20  
  Purchase #2 $234.63   12.170%   $263.1845   $263.18   $263.20   $263.20  
  Purchase #3 $179.44   9.234%   $196.0095   $196.01   $196.00   $196.00  
  Purchase #4 $18.53   11.295%   $20.623   $20.62   $20.60   $20.60  
  Purchase #5 $149.80   6.249%   $159.161   $159.16   $159.15   $159.20  
  Purchase #6 $46.64   5.687%   $49.2924   $49.29   $49.30   $49.30  
  Purchase #7 $49.80   4.732%   $52.1565   $52.16   $52.15   $52.20  
  7 purchase totals = $793.23       $863.6181   $863.61   $863.60   $863.70