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 $107.33   6.808%   $114.637   $114.64   $114.65   $114.60  
  Purchase #2 $37.88   3.850%   $39.3384   $39.34   $39.35   $39.30  
  Purchase #3 $129.71   3.583%   $134.3575   $134.36   $134.35   $134.40  
  Purchase #4 $208.77   13.325%   $236.5886   $236.59   $236.60   $236.60  
  Purchase #5 $5.55   11.519%   $6.1893   $6.19   $6.20   $6.20  
  Purchase #6 $194.77   3.604%   $201.7895   $201.79   $201.80   $201.80  
  Purchase #7 $52.54   3.855%   $54.5654   $54.57   $54.55   $54.60  
  7 purchase totals = $736.55       $787.4657   $787.48   $787.50   $787.50