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 $233.70   12.476%   $262.8564   $262.86   $262.85   $262.90  
  Purchase #2 $220.70   10.168%   $243.1408   $243.14   $243.15   $243.10  
  Purchase #3 $64.66   7.821%   $69.7171   $69.72   $69.70   $69.70  
  Purchase #4 $149.91   4.404%   $156.512   $156.51   $156.50   $156.50  
  Purchase #5 $226.69   10.233%   $249.8872   $249.89   $249.90   $249.90  
  Purchase #6 $70.39   10.204%   $77.5726   $77.57   $77.55   $77.60  
  Purchase #7 $101.36   7.103%   $108.5596   $108.56   $108.55   $108.60  
  7 purchase totals = $1,067.41       $1,168.2457   $1,168.25   $1,168.20   $1,168.30