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	$245.44	3.436%	$253.8733	$253.87	$253.85	$253.90
Purchase #2	$235.57	12.417%	$264.8207	$264.82	$264.80	$264.80
Purchase #3	$50.59	9.827%	$55.5615	$55.56	$55.55	$55.60
Purchase #4	$77.99	9.133%	$85.1128	$85.11	$85.10	$85.10
Purchase #5	$59.34	7.233%	$63.6321	$63.63	$63.65	$63.60
Purchase #6	$157.61	10.820%	$174.6634	$174.66	$174.65	$174.70
Purchase #7	$216.27	8.158%	$233.9133	$233.91	$233.90	$233.90
7 purchase totals =	$1,042.81		$1,131.5771	$1,131.56	$1,131.50	$1,131.60