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 $60.94   11.545%   $67.9755   $67.98   $68.00   $68.00  
  Purchase #2 $189.86   12.185%   $212.9944   $212.99   $213.00   $213.00  
  Purchase #3 $218.91   12.603%   $246.4992   $246.50   $246.50   $246.50  
  Purchase #4 $121.33   12.623%   $136.6455   $136.65   $136.65   $136.60  
  Purchase #5 $144.68   5.311%   $152.364   $152.36   $152.35   $152.40  
  Purchase #6 $178.37   12.457%   $200.5896   $200.59   $200.60   $200.60  
  Purchase #7 $214.95   3.276%   $221.9918   $221.99   $222.00   $222.00  
  7 purchase totals = $1,129.04       $1,239.0600   $1,239.06   $1,239.10   $1,239.10