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	$126.38	5.710%	$133.5963	$133.60	$133.60	$133.60
Purchase #2	$96.82	5.462%	$102.1083	$102.11	$102.10	$102.10
Purchase #3	$142.51	4.399%	$148.779	$148.78	$148.80	$148.80
Purchase #4	$80.56	11.685%	$89.9734	$89.97	$89.95	$90.00
Purchase #5	$99.59	3.334%	$102.9103	$102.91	$102.90	$102.90
Purchase #6	$152.59	8.599%	$165.7112	$165.71	$165.70	$165.70
Purchase #7	$80.70	10.336%	$89.0412	$89.04	$89.05	$89.00
7 purchase totals =	$779.15		$832.1197	$832.12	$832.10	$832.10