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 $208.38   13.281%   $236.0549   $236.05   $236.05   $236.10  
  Purchase #2 $59.72   4.615%   $62.4761   $62.48   $62.50   $62.50  
  Purchase #3 $238.31   10.479%   $263.2825   $263.28   $263.30   $263.30  
  Purchase #4 $193.32   7.136%   $207.1153   $207.12   $207.10   $207.10  
  Purchase #5 $88.77   11.859%   $99.2972   $99.30   $99.30   $99.30  
  Purchase #6 $190.28   8.554%   $206.5566   $206.56   $206.55   $206.60  
  Purchase #7 $214.98   4.299%   $224.222   $224.22   $224.20   $224.20  
  7 purchase totals = $1,193.76       $1,299.0046   $1,299.01   $1,299.00   $1,299.10