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 $30.47   6.178%   $32.3524   $32.35   $32.35   $32.40  
  Purchase #2 $216.40   9.328%   $236.5858   $236.59   $236.60   $236.60  
  Purchase #3 $60.62   4.638%   $63.4316   $63.43   $63.45   $63.40  
  Purchase #4 $37.45   10.385%   $41.3392   $41.34   $41.35   $41.30  
  Purchase #5 $233.91   4.152%   $243.6219   $243.62   $243.60   $243.60  
  Purchase #6 $153.57   11.601%   $171.3857   $171.39   $171.40   $171.40  
  Purchase #7 $33.69   12.833%   $38.0134   $38.01   $38.00   $38.00  
  7 purchase totals = $766.11       $826.7300   $826.73   $826.75   $826.70