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 $152.36   11.443%   $169.7946   $169.79   $169.80   $169.80  
  Purchase #2 $240.93   5.652%   $254.5474   $254.55   $254.55   $254.50  
  Purchase #3 $225.47   12.756%   $254.231   $254.23   $254.25   $254.20  
  Purchase #4 $114.60   7.674%   $123.3944   $123.39   $123.40   $123.40  
  Purchase #5 $75.25   5.790%   $79.607   $79.61   $79.60   $79.60  
  Purchase #6 $115.42   8.797%   $125.5735   $125.57   $125.55   $125.60  
  Purchase #7 $35.32   11.280%   $39.3041   $39.30   $39.30   $39.30  
  7 purchase totals = $959.35       $1,046.4520   $1,046.44   $1,046.45   $1,046.40