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 $60.41   12.873%   $68.1866   $68.19   $68.20   $68.20  
  Purchase #2 $213.45   11.624%   $238.2614   $238.26   $238.25   $238.30  
  Purchase #3 $105.43   13.592%   $119.76   $119.76   $119.75   $119.80  
  Purchase #4 $232.73   8.796%   $253.2009   $253.20   $253.20   $253.20  
  Purchase #5 $44.85   5.650%   $47.384   $47.38   $47.40   $47.40  
  Purchase #6 $184.52   4.693%   $193.1795   $193.18   $193.20   $193.20  
  Purchase #7 $247.54   9.362%   $270.7147   $270.71   $270.70   $270.70  
  7 purchase totals = $1,088.93       $1,190.6871   $1,190.68   $1,190.70   $1,190.80