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	$243.39	12.537%	$273.9038	$273.90	$273.90	$273.90
Purchase #2	$80.76	6.794%	$86.2468	$86.25	$86.25	$86.20
Purchase #3	$142.32	13.681%	$161.7908	$161.79	$161.80	$161.80
Purchase #4	$61.90	5.502%	$65.3057	$65.31	$65.30	$65.30
Purchase #5	$57.81	13.796%	$65.7855	$65.79	$65.80	$65.80
Purchase #6	$36.32	12.274%	$40.7779	$40.78	$40.80	$40.80
Purchase #7	$86.44	7.148%	$92.6187	$92.62	$92.60	$92.60
7 purchase totals =	$708.94		$786.4292	$786.44	$786.45	$786.40