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 $86.33   11.323%   $96.1051   $96.11   $96.10   $96.10  
  Purchase #2 $111.62   3.756%   $115.8124   $115.81   $115.80   $115.80  
  Purchase #3 $145.80   13.678%   $165.7425   $165.74   $165.75   $165.70  
  Purchase #4 $119.65   3.512%   $123.8521   $123.85   $123.85   $123.90  
  Purchase #5 $86.31   12.702%   $97.2731   $97.27   $97.25   $97.30  
  Purchase #6 $95.98   9.144%   $104.7564   $104.76   $104.75   $104.80  
  Purchase #7 $166.28   12.596%   $187.2246   $187.22   $187.20   $187.20  
  7 purchase totals = $811.97       $890.7662   $890.76   $890.70   $890.80