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 $234.74   13.345%   $266.0661   $266.07   $266.05   $266.10  
  Purchase #2 $244.57   6.304%   $259.9877   $259.99   $260.00   $260.00  
  Purchase #3 $39.33   13.671%   $44.7068   $44.71   $44.70   $44.70  
  Purchase #4 $92.55   7.321%   $99.3256   $99.33   $99.35   $99.30  
  Purchase #5 $228.55   8.467%   $247.9013   $247.90   $247.90   $247.90  
  Purchase #6 $27.60   12.127%   $30.9471   $30.95   $30.95   $30.90  
  Purchase #7 $100.90   5.474%   $106.4233   $106.42   $106.40   $106.40  
  7 purchase totals = $968.24       $1,055.3579   $1,055.37   $1,055.35   $1,055.30