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 $23.44   12.830%   $26.4474   $26.45   $26.45   $26.40  
  Purchase #2 $159.68   8.146%   $172.6875   $172.69   $172.70   $172.70  
  Purchase #3 $209.46   4.812%   $219.5392   $219.54   $219.55   $219.50  
  Purchase #4 $241.88   3.592%   $250.5683   $250.57   $250.55   $250.60  
  Purchase #5 $187.96   4.255%   $195.9577   $195.96   $195.95   $196.00  
  Purchase #6 $127.54   3.493%   $131.995   $132.00   $132.00   $132.00  
  Purchase #7 $121.73   11.481%   $135.7058   $135.71   $135.70   $135.70  
  7 purchase totals = $1,071.69       $1,132.9009   $1,132.92   $1,132.90   $1,132.90