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 $58.78   12.356%   $66.0429   $66.04   $66.05   $66.00  
  Purchase #2 $188.93   5.452%   $199.2305   $199.23   $199.25   $199.20  
  Purchase #3 $146.85   10.342%   $162.0372   $162.04   $162.05   $162.00  
  Purchase #4 $246.38   7.842%   $265.7011   $265.70   $265.70   $265.70  
  Purchase #5 $244.44   5.700%   $258.3731   $258.37   $258.35   $258.40  
  Purchase #6 $6.28   8.758%   $6.83   $6.83   $6.85   $6.80  
  Purchase #7 $185.79   5.795%   $196.5565   $196.56   $196.55   $196.60  
  7 purchase totals = $1,077.45       $1,154.7713   $1,154.77   $1,154.80   $1,154.70