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 $204.38   9.773%   $224.3541   $224.35   $224.35   $224.40  
  Purchase #2 $35.97   3.275%   $37.148   $37.15   $37.15   $37.10  
  Purchase #3 $190.52   5.771%   $201.5149   $201.51   $201.50   $201.50  
  Purchase #4 $66.38   13.788%   $75.5325   $75.53   $75.55   $75.50  
  Purchase #5 $186.81   12.573%   $210.2976   $210.30   $210.30   $210.30  
  Purchase #6 $95.42   3.465%   $98.7263   $98.73   $98.75   $98.70  
  Purchase #7 $212.26   7.613%   $228.4194   $228.42   $228.40   $228.40  
  7 purchase totals = $991.74       $1,075.9928   $1,075.99   $1,076.00   $1,075.90