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 $24.60   8.450%   $26.6787   $26.68   $26.70   $26.70  
  Purchase #2 $232.85   9.325%   $254.5633   $254.56   $254.55   $254.60  
  Purchase #3 $52.80   11.721%   $58.9887   $58.99   $59.00   $59.00  
  Purchase #4 $223.76   10.431%   $247.1004   $247.10   $247.10   $247.10  
  Purchase #5 $191.59   8.767%   $208.3867   $208.39   $208.40   $208.40  
  Purchase #6 $206.58   4.603%   $216.0889   $216.09   $216.10   $216.10  
  Purchase #7 $208.70   6.727%   $222.7392   $222.74   $222.75   $222.70  
  7 purchase totals = $1,140.88       $1,234.5459   $1,234.55   $1,234.60   $1,234.60