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 $194.33   4.702%   $203.4674   $203.47   $203.45   $203.50  
  Purchase #2 $231.48   13.645%   $263.0654   $263.07   $263.05   $263.10  
  Purchase #3 $117.37   8.266%   $127.0718   $127.07   $127.05   $127.10  
  Purchase #4 $86.64   7.372%   $93.0271   $93.03   $93.05   $93.00  
  Purchase #5 $185.89   8.218%   $201.1664   $201.17   $201.15   $201.20  
  Purchase #6 $241.94   3.539%   $250.5023   $250.50   $250.50   $250.50  
  Purchase #7 $98.77   8.717%   $107.3798   $107.38   $107.40   $107.40  
  7 purchase totals = $1,156.42       $1,245.6802   $1,245.69   $1,245.65   $1,245.80