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 $48.62   8.874%   $52.9345   $52.93   $52.95   $52.90  
  Purchase #2 $93.72   12.646%   $105.5718   $105.57   $105.55   $105.60  
  Purchase #3 $211.63   3.487%   $219.0095   $219.01   $219.00   $219.00  
  Purchase #4 $240.58   10.700%   $266.3221   $266.32   $266.30   $266.30  
  Purchase #5 $93.73   11.197%   $104.2249   $104.22   $104.20   $104.20  
  Purchase #6 $40.51   11.514%   $45.1743   $45.17   $45.15   $45.20  
  Purchase #7 $105.47   8.117%   $114.031   $114.03   $114.05   $114.00  
  7 purchase totals = $834.26       $907.2681   $907.25   $907.20   $907.20