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 $114.96   3.501%   $118.9847   $118.98   $119.00   $119.00  
  Purchase #2 $240.30   10.433%   $265.3705   $265.37   $265.35   $265.40  
  Purchase #3 $143.81   10.685%   $159.1761   $159.18   $159.20   $159.20  
  Purchase #4 $141.83   3.829%   $147.2607   $147.26   $147.25   $147.30  
  Purchase #5 $38.69   13.463%   $43.8988   $43.90   $43.90   $43.90  
  Purchase #6 $187.78   8.738%   $204.1882   $204.19   $204.20   $204.20  
  Purchase #7 $14.48   12.821%   $16.3365   $16.34   $16.35   $16.30  
  7 purchase totals = $881.85       $955.2155   $955.22   $955.25   $955.30