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 $91.98   3.704%   $95.3869   $95.39   $95.40   $95.40  
  Purchase #2 $149.27   12.270%   $167.5854   $167.59   $167.60   $167.60  
  Purchase #3 $239.81   6.159%   $254.5799   $254.58   $254.60   $254.60  
  Purchase #4 $177.47   3.403%   $183.5093   $183.51   $183.50   $183.50  
  Purchase #5 $114.80   13.180%   $129.9306   $129.93   $129.95   $129.90  
  Purchase #6 $44.56   6.651%   $47.5237   $47.52   $47.50   $47.50  
  Purchase #7 $235.41   11.174%   $261.7147   $261.71   $261.70   $261.70  
  7 purchase totals = $1,053.30       $1,140.2305   $1,140.23   $1,140.25   $1,140.20