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	$25.46	10.675%	$28.1779	$28.18	$28.20	$28.20
Purchase #2	$250.85	4.858%	$263.0363	$263.04	$263.05	$263.00
Purchase #3	$130.75	13.127%	$147.9136	$147.91	$147.90	$147.90
Purchase #4	$29.33	10.516%	$32.4143	$32.41	$32.40	$32.40
Purchase #5	$37.42	3.741%	$38.8199	$38.82	$38.80	$38.80
Purchase #6	$245.63	4.430%	$256.5114	$256.51	$256.50	$256.50
Purchase #7	$220.97	7.748%	$238.0908	$238.09	$238.10	$238.10
7 purchase totals =	$940.41		$1,004.9642	$1,004.96	$1,004.95	$1,004.90