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 $230.92   13.233%   $261.4776   $261.48   $261.50   $261.50  
  Purchase #2 $216.92   9.684%   $237.9265   $237.93   $237.95   $237.90  
  Purchase #3 $106.91   12.311%   $120.0717   $120.07   $120.05   $120.10  
  Purchase #4 $169.94   7.852%   $183.2837   $183.28   $183.30   $183.30  
  Purchase #5 $43.58   8.362%   $47.2242   $47.22   $47.20   $47.20  
  Purchase #6 $5.65   7.621%   $6.0806   $6.08   $6.10   $6.10  
  Purchase #7 $185.25   10.593%   $204.8735   $204.87   $204.85   $204.90  
  7 purchase totals = $959.17       $1,060.9378   $1,060.93   $1,060.95   $1,061.00