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	$31.62	3.772%	$32.8127	$32.81	$32.80	$32.80
Purchase #2	$149.93	7.148%	$160.647	$160.65	$160.65	$160.60
Purchase #3	$181.86	9.510%	$199.1549	$199.15	$199.15	$199.20
Purchase #4	$182.62	4.197%	$190.2846	$190.28	$190.30	$190.30
Purchase #5	$221.88	12.585%	$249.8036	$249.80	$249.80	$249.80
Purchase #6	$65.53	12.521%	$73.735	$73.74	$73.75	$73.70
Purchase #7	$63.77	12.749%	$71.9	$71.90	$71.90	$71.90
7 purchase totals =	$897.21		$978.3378	$978.33	$978.35	$978.30