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 $60.88   13.642%   $69.1852   $69.19   $69.20   $69.20  
  Purchase #2 $150.73   5.197%   $158.5634   $158.56   $158.55   $158.60  
  Purchase #3 $114.26   8.227%   $123.6602   $123.66   $123.65   $123.70  
  Purchase #4 $54.33   6.643%   $57.9391   $57.94   $57.95   $57.90  
  Purchase #5 $64.50   6.417%   $68.639   $68.64   $68.65   $68.60  
  Purchase #6 $57.73   9.546%   $63.2409   $63.24   $63.25   $63.20  
  Purchase #7 $242.67   8.539%   $263.3916   $263.39   $263.40   $263.40  
  7 purchase totals = $745.10       $804.6194   $804.62   $804.65   $804.60