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 $94.28   9.851%   $103.5675   $103.57   $103.55   $103.60  
  Purchase #2 $229.84   13.213%   $260.2088   $260.21   $260.20   $260.20  
  Purchase #3 $249.91   12.719%   $281.6961   $281.70   $281.70   $281.70  
  Purchase #4 $42.33   10.373%   $46.7209   $46.72   $46.70   $46.70  
  Purchase #5 $221.25   10.861%   $245.28   $245.28   $245.30   $245.30  
  Purchase #6 $111.86   12.597%   $125.951   $125.95   $125.95   $126.00  
  Purchase #7 $175.70   10.213%   $193.6442   $193.64   $193.65   $193.60  
  7 purchase totals = $1,125.17       $1,257.0685   $1,257.07   $1,257.05   $1,257.10