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 $59.77   11.712%   $66.7703   $66.77   $66.75   $66.80  
  Purchase #2 $111.78   4.398%   $116.6961   $116.70   $116.70   $116.70  
  Purchase #3 $233.34   11.637%   $260.4938   $260.49   $260.50   $260.50  
  Purchase #4 $120.89   10.704%   $133.8301   $133.83   $133.85   $133.80  
  Purchase #5 $148.51   9.445%   $162.5368   $162.54   $162.55   $162.50  
  Purchase #6 $234.30   8.567%   $254.3725   $254.37   $254.35   $254.40  
  Purchase #7 $114.39   13.648%   $130.0019   $130.00   $130.00   $130.00  
  7 purchase totals = $1,022.98       $1,124.7015   $1,124.70   $1,124.70   $1,124.70