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	$60.35	7.306%	$64.7592	$64.76	$64.75	$64.80
Purchase #2	$146.63	3.846%	$152.2694	$152.27	$152.25	$152.30
Purchase #3	$133.78	5.857%	$141.6155	$141.62	$141.60	$141.60
Purchase #4	$81.60	4.148%	$84.9848	$84.98	$85.00	$85.00
Purchase #5	$63.59	11.323%	$70.7903	$70.79	$70.80	$70.80
Purchase #6	$185.94	5.213%	$195.6331	$195.63	$195.65	$195.60
Purchase #7	$81.57	10.700%	$90.298	$90.30	$90.30	$90.30
7 purchase totals =	$753.46		$800.3503	$800.35	$800.35	$800.40