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 $24.91   8.170%   $26.9451   $26.95   $26.95   $26.90  
  Purchase #2 $183.64   7.577%   $197.5544   $197.55   $197.55   $197.60  
  Purchase #3 $56.95   5.363%   $60.0042   $60.00   $60.00   $60.00  
  Purchase #4 $170.30   11.530%   $189.9356   $189.94   $189.95   $189.90  
  Purchase #5 $213.48   13.840%   $243.0256   $243.03   $243.05   $243.00  
  Purchase #6 $239.78   12.675%   $270.1721   $270.17   $270.15   $270.20  
  Purchase #7 $238.43   11.185%   $265.0984   $265.10   $265.10   $265.10  
  7 purchase totals = $1,127.49       $1,252.7354   $1,252.74   $1,252.75   $1,252.70