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 $59.85   10.723%   $66.2677   $66.27   $66.25   $66.30  
  Purchase #2 $94.99   9.297%   $103.8212   $103.82   $103.80   $103.80  
  Purchase #3 $197.40   11.150%   $219.4101   $219.41   $219.40   $219.40  
  Purchase #4 $104.45   9.653%   $114.5326   $114.53   $114.55   $114.50  
  Purchase #5 $45.75   3.241%   $47.2328   $47.23   $47.25   $47.20  
  Purchase #6 $185.89   11.666%   $207.5759   $207.58   $207.60   $207.60  
  Purchase #7 $243.28   7.606%   $261.7839   $261.78   $261.80   $261.80  
  7 purchase totals = $931.61       $1,020.6242   $1,020.62   $1,020.65   $1,020.60