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 $242.59   8.402%   $262.9724   $262.97   $262.95   $263.00  
  Purchase #2 $190.46   8.346%   $206.3558   $206.36   $206.35   $206.40  
  Purchase #3 $23.50   6.698%   $25.074   $25.07   $25.05   $25.10  
  Purchase #4 $203.55   5.373%   $214.4867   $214.49   $214.50   $214.50  
  Purchase #5 $11.35   5.280%   $11.9493   $11.95   $11.95   $11.90  
  Purchase #6 $99.59   12.529%   $112.0676   $112.07   $112.05   $112.10  
  Purchase #7 $159.93   11.269%   $177.9525   $177.95   $177.95   $178.00  
  7 purchase totals = $930.97       $1,010.8583   $1,010.86   $1,010.80   $1,011.00