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 $202.26   12.182%   $226.8993   $226.90   $226.90   $226.90  
  Purchase #2 $165.81   7.399%   $178.0783   $178.08   $178.10   $178.10  
  Purchase #3 $238.78   4.563%   $249.6755   $249.68   $249.70   $249.70  
  Purchase #4 $185.54   5.104%   $195.01   $195.01   $195.00   $195.00  
  Purchase #5 $48.44   4.307%   $50.5263   $50.53   $50.55   $50.50  
  Purchase #6 $167.51   5.418%   $176.5857   $176.59   $176.60   $176.60  
  Purchase #7 $160.60   11.715%   $179.4143   $179.41   $179.40   $179.40  
  7 purchase totals = $1,168.94       $1,256.1894   $1,256.20   $1,256.25   $1,256.20