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	$51.58	8.152%	$55.7848	$55.78	$55.80	$55.80
Purchase #2	$85.36	4.830%	$89.4829	$89.48	$89.50	$89.50
Purchase #3	$26.54	8.117%	$28.6943	$28.69	$28.70	$28.70
Purchase #4	$169.28	12.398%	$190.2673	$190.27	$190.25	$190.30
Purchase #5	$197.57	12.794%	$222.8471	$222.85	$222.85	$222.80
Purchase #6	$190.77	11.254%	$212.2393	$212.24	$212.25	$212.20
Purchase #7	$117.48	11.383%	$130.8527	$130.85	$130.85	$130.90
7 purchase totals =	$838.58		$930.1684	$930.16	$930.20	$930.20