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	$115.76	10.192%	$127.5583	$127.56	$127.55	$127.60
Purchase #2	$202.90	8.291%	$219.7224	$219.72	$219.70	$219.70
Purchase #3	$219.57	10.774%	$243.2265	$243.23	$243.25	$243.20
Purchase #4	$209.52	13.722%	$238.2703	$238.27	$238.25	$238.30
Purchase #5	$97.79	11.472%	$109.0085	$109.01	$109.00	$109.00
Purchase #6	$27.81	3.282%	$28.7227	$28.72	$28.70	$28.70
Purchase #7	$249.70	10.543%	$276.0259	$276.03	$276.05	$276.00
7 purchase totals =	$1,123.05		$1,242.5346	$1,242.54	$1,242.50	$1,242.50