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 $64.69   8.116%   $69.9402   $69.94   $69.95   $69.90  
  Purchase #2 $168.95   9.123%   $184.3633   $184.36   $184.35   $184.40  
  Purchase #3 $247.47   11.300%   $275.4341   $275.43   $275.45   $275.40  
  Purchase #4 $101.82   12.429%   $114.4752   $114.48   $114.50   $114.50  
  Purchase #5 $107.70   13.811%   $122.5744   $122.57   $122.55   $122.60  
  Purchase #6 $166.93   8.289%   $180.7668   $180.77   $180.75   $180.80  
  Purchase #7 $207.25   3.184%   $213.8488   $213.85   $213.85   $213.80  
  7 purchase totals = $1,064.81       $1,161.4028   $1,161.40   $1,161.40   $1,161.40