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 $231.35   10.547%   $255.7505   $255.75   $255.75   $255.80  
  Purchase #2 $88.83   8.586%   $96.4569   $96.46   $96.45   $96.50  
  Purchase #3 $88.44   10.627%   $97.8385   $97.84   $97.85   $97.80  
  Purchase #4 $196.38   5.634%   $207.444   $207.44   $207.45   $207.40  
  Purchase #5 $48.64   10.800%   $53.8931   $53.89   $53.90   $53.90  
  Purchase #6 $241.80   9.501%   $264.7734   $264.77   $264.75   $264.80  
  Purchase #7 $70.64   12.548%   $79.5039   $79.50   $79.50   $79.50  
  7 purchase totals = $966.08       $1,055.6603   $1,055.65   $1,055.65   $1,055.70