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 $69.86   3.805%   $72.5182   $72.52   $72.50   $72.50  
  Purchase #2 $15.50   3.526%   $16.0465   $16.05   $16.05   $16.00  
  Purchase #3 $225.26   10.463%   $248.829   $248.83   $248.85   $248.80  
  Purchase #4 $80.84   7.572%   $86.9612   $86.96   $86.95   $87.00  
  Purchase #5 $246.55   5.873%   $261.0299   $261.03   $261.05   $261.00  
  Purchase #6 $162.39   6.320%   $172.653   $172.65   $172.65   $172.70  
  Purchase #7 $133.90   4.819%   $140.3526   $140.35   $140.35   $140.40  
  7 purchase totals = $934.30       $998.3904   $998.39   $998.40   $998.40