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 $248.97   13.495%   $282.5685   $282.57   $282.55   $282.60  
  Purchase #2 $74.78   11.227%   $83.1756   $83.18   $83.20   $83.20  
  Purchase #3 $241.74   9.445%   $264.5723   $264.57   $264.55   $264.60  
  Purchase #4 $95.87   5.209%   $100.8639   $100.86   $100.85   $100.90  
  Purchase #5 $249.56   5.624%   $263.5953   $263.60   $263.60   $263.60  
  Purchase #6 $86.28   11.839%   $96.4947   $96.49   $96.50   $96.50  
  Purchase #7 $203.92   3.436%   $210.9267   $210.93   $210.95   $210.90  
  7 purchase totals = $1,201.12       $1,302.1970   $1,302.20   $1,302.20   $1,302.30