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 $69.41   5.836%   $73.4608   $73.46   $73.45   $73.50  
  Purchase #2 $102.26   9.399%   $111.8714   $111.87   $111.85   $111.90  
  Purchase #3 $167.39   7.767%   $180.3912   $180.39   $180.40   $180.40  
  Purchase #4 $16.79   9.731%   $18.4238   $18.42   $18.40   $18.40  
  Purchase #5 $114.94   5.513%   $121.2766   $121.28   $121.30   $121.30  
  Purchase #6 $171.84   4.548%   $179.6553   $179.66   $179.65   $179.70  
  Purchase #7 $85.36   4.594%   $89.2814   $89.28   $89.30   $89.30  
  7 purchase totals = $727.99       $774.3605   $774.36   $774.35   $774.50