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 $245.76   6.257%   $261.1372   $261.14   $261.15   $261.10  
  Purchase #2 $61.68   11.382%   $68.7004   $68.70   $68.70   $68.70  
  Purchase #3 $86.57   9.666%   $94.9379   $94.94   $94.95   $94.90  
  Purchase #4 $92.60   13.666%   $105.2547   $105.25   $105.25   $105.30  
  Purchase #5 $53.93   11.278%   $60.0122   $60.01   $60.00   $60.00  
  Purchase #6 $150.64   11.240%   $167.5719   $167.57   $167.55   $167.60  
  Purchase #7 $246.47   11.213%   $274.1067   $274.11   $274.10   $274.10  
  7 purchase totals = $937.65       $1,031.7210   $1,031.72   $1,031.70   $1,031.70