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 $241.59   11.476%   $269.3149   $269.31   $269.30   $269.30  
  Purchase #2 $165.74   4.707%   $173.5414   $173.54   $173.55   $173.50  
  Purchase #3 $54.33   11.369%   $60.5068   $60.51   $60.50   $60.50  
  Purchase #4 $94.78   3.779%   $98.3617   $98.36   $98.35   $98.40  
  Purchase #5 $235.69   13.744%   $268.0832   $268.08   $268.10   $268.10  
  Purchase #6 $164.47   4.457%   $171.8004   $171.80   $171.80   $171.80  
  Purchase #7 $226.91   7.284%   $243.4381   $243.44   $243.45   $243.40  
  7 purchase totals = $1,183.51       $1,285.0465   $1,285.04   $1,285.05   $1,285.00