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 $247.62   11.489%   $276.0691   $276.07   $276.05   $276.10  
  Purchase #2 $173.68   13.154%   $196.5259   $196.53   $196.55   $196.50  
  Purchase #3 $151.37   10.363%   $167.0565   $167.06   $167.05   $167.10  
  Purchase #4 $158.62   6.316%   $168.6384   $168.64   $168.65   $168.60  
  Purchase #5 $150.48   12.151%   $168.7648   $168.76   $168.75   $168.80  
  Purchase #6 $249.25   7.688%   $268.4123   $268.41   $268.40   $268.40  
  Purchase #7 $64.57   6.271%   $68.6192   $68.62   $68.60   $68.60  
  7 purchase totals = $1,195.59       $1,314.0862   $1,314.09   $1,314.05   $1,314.10