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 $108.78   10.252%   $119.9321   $119.93   $119.95   $119.90  
  Purchase #2 $33.28   8.194%   $36.007   $36.01   $36.00   $36.00  
  Purchase #3 $176.41   9.812%   $193.7193   $193.72   $193.70   $193.70  
  Purchase #4 $214.84   13.473%   $243.7854   $243.79   $243.80   $243.80  
  Purchase #5 $70.40   4.186%   $73.3469   $73.35   $73.35   $73.30  
  Purchase #6 $6.47   8.592%   $7.0259   $7.03   $7.05   $7.00  
  Purchase #7 $92.27   8.808%   $100.3971   $100.40   $100.40   $100.40  
  7 purchase totals = $702.45       $774.2137   $774.23   $774.25   $774.10