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 $147.27   12.398%   $165.5285   $165.53   $165.55   $165.50  
  Purchase #2 $15.27   8.322%   $16.5408   $16.54   $16.55   $16.50  
  Purchase #3 $89.77   8.122%   $97.0611   $97.06   $97.05   $97.10  
  Purchase #4 $48.54   10.823%   $53.7935   $53.79   $53.80   $53.80  
  Purchase #5 $120.59   4.488%   $126.0021   $126.00   $126.00   $126.00  
  Purchase #6 $208.27   11.521%   $232.2648   $232.26   $232.25   $232.30  
  Purchase #7 $20.99   11.516%   $23.4072   $23.41   $23.40   $23.40  
  7 purchase totals = $650.70       $714.5980   $714.59   $714.60   $714.60