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 $176.61   10.481%   $195.1205   $195.12   $195.10   $195.10  
  Purchase #2 $40.77   12.431%   $45.8381   $45.84   $45.85   $45.80  
  Purchase #3 $240.66   9.280%   $262.9932   $262.99   $263.00   $263.00  
  Purchase #4 $40.44   7.396%   $43.4309   $43.43   $43.45   $43.40  
  Purchase #5 $77.80   8.796%   $84.6433   $84.64   $84.65   $84.60  
  Purchase #6 $57.26   6.312%   $60.8743   $60.87   $60.85   $60.90  
  Purchase #7 $224.39   7.585%   $241.41   $241.41   $241.40   $241.40  
  7 purchase totals = $857.93       $934.3103   $934.30   $934.30   $934.20