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	$111.73	11.773%	$124.884	$124.88	$124.90	$124.90
Purchase #2	$131.87	4.234%	$137.4534	$137.45	$137.45	$137.50
Purchase #3	$136.40	11.423%	$151.981	$151.98	$152.00	$152.00
Purchase #4	$28.92	10.201%	$31.8701	$31.87	$31.85	$31.90
Purchase #5	$171.73	10.124%	$189.1159	$189.12	$189.10	$189.10
Purchase #6	$56.70	9.424%	$62.0434	$62.04	$62.05	$62.00
Purchase #7	$222.48	11.276%	$247.5668	$247.57	$247.55	$247.60
7 purchase totals =	$859.83		$944.9146	$944.91	$944.90	$945.00