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 $209.48   12.441%   $235.5414   $235.54   $235.55   $235.50  
  Purchase #2 $183.95   7.218%   $197.2275   $197.23   $197.25   $197.20  
  Purchase #3 $34.42   3.149%   $35.5039   $35.50   $35.50   $35.50  
  Purchase #4 $216.83   7.702%   $233.5302   $233.53   $233.55   $233.50  
  Purchase #5 $63.26   4.203%   $65.9188   $65.92   $65.90   $65.90  
  Purchase #6 $105.54   11.320%   $117.4871   $117.49   $117.50   $117.50  
  Purchase #7 $140.98   13.460%   $159.9559   $159.96   $159.95   $160.00  
  7 purchase totals = $954.46       $1,045.1648   $1,045.17   $1,045.20   $1,045.10