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	$201.69	9.557%	$220.9655	$220.97	$220.95	$221.00
Purchase #2	$83.97	5.860%	$88.8906	$88.89	$88.90	$88.90
Purchase #3	$89.74	7.427%	$96.405	$96.41	$96.40	$96.40
Purchase #4	$160.98	12.772%	$181.5404	$181.54	$181.55	$181.50
Purchase #5	$91.42	13.110%	$103.4052	$103.41	$103.40	$103.40
Purchase #6	$162.62	3.539%	$168.3751	$168.38	$168.40	$168.40
Purchase #7	$57.80	3.259%	$59.6837	$59.68	$59.70	$59.70
7 purchase totals =	$848.22		$919.2655	$919.28	$919.30	$919.30