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 $147.96   13.733%   $168.2793   $168.28   $168.30   $168.30  
  Purchase #2 $53.99   8.689%   $58.6812   $58.68   $58.70   $58.70  
  Purchase #3 $215.44   8.113%   $232.9186   $232.92   $232.90   $232.90  
  Purchase #4 $219.78   4.766%   $230.2547   $230.25   $230.25   $230.30  
  Purchase #5 $134.97   9.424%   $147.6896   $147.69   $147.70   $147.70  
  Purchase #6 $242.86   4.717%   $254.3157   $254.32   $254.30   $254.30  
  Purchase #7 $209.34   3.405%   $216.468   $216.47   $216.45   $216.50  
  7 purchase totals = $1,224.34       $1,308.6071   $1,308.61   $1,308.60   $1,308.70