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 $176.28   13.256%   $199.6477   $199.65   $199.65   $199.60  
  Purchase #2 $25.95   13.183%   $29.371   $29.37   $29.35   $29.40  
  Purchase #3 $8.62   5.613%   $9.1038   $9.10   $9.10   $9.10  
  Purchase #4 $225.93   9.789%   $248.0463   $248.05   $248.05   $248.00  
  Purchase #5 $34.49   5.839%   $36.5039   $36.50   $36.50   $36.50  
  Purchase #6 $148.92   12.561%   $167.6258   $167.63   $167.65   $167.60  
  Purchase #7 $63.98   7.842%   $68.9973   $69.00   $69.00   $69.00  
  7 purchase totals = $684.17       $759.2958   $759.30   $759.30   $759.20