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 $171.88   6.212%   $182.5572   $182.56   $182.55   $182.60  
  Purchase #2 $63.65   3.437%   $65.8377   $65.84   $65.85   $65.80  
  Purchase #3 $228.57   5.398%   $240.9082   $240.91   $240.90   $240.90  
  Purchase #4 $74.87   4.734%   $78.4143   $78.41   $78.40   $78.40  
  Purchase #5 $226.44   12.552%   $254.8627   $254.86   $254.85   $254.90  
  Purchase #6 $109.37   9.136%   $119.362   $119.36   $119.35   $119.40  
  Purchase #7 $75.49   5.260%   $79.4608   $79.46   $79.45   $79.50  
  7 purchase totals = $950.27       $1,021.4029   $1,021.40   $1,021.35   $1,021.50