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 $45.84   3.199%   $47.3064   $47.31   $47.30   $47.30  
  Purchase #2 $239.94   12.141%   $269.0711   $269.07   $269.05   $269.10  
  Purchase #3 $64.94   4.391%   $67.7915   $67.79   $67.80   $67.80  
  Purchase #4 $249.62   12.606%   $281.0871   $281.09   $281.10   $281.10  
  Purchase #5 $85.44   10.759%   $94.6325   $94.63   $94.65   $94.60  
  Purchase #6 $196.62   5.335%   $207.1097   $207.11   $207.10   $207.10  
  Purchase #7 $48.91   7.483%   $52.5699   $52.57   $52.55   $52.60  
  7 purchase totals = $931.31       $1,019.5682   $1,019.57   $1,019.55   $1,019.60