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	$203.55	4.415%	$212.5367	$212.54	$212.55	$212.50
Purchase #2	$17.46	10.238%	$19.2476	$19.25	$19.25	$19.20
Purchase #3	$112.87	9.192%	$123.245	$123.25	$123.25	$123.20
Purchase #4	$198.58	5.203%	$208.9121	$208.91	$208.90	$208.90
Purchase #5	$80.63	10.133%	$88.8002	$88.80	$88.80	$88.80
Purchase #6	$83.89	7.221%	$89.9477	$89.95	$89.95	$89.90
Purchase #7	$229.62	9.148%	$250.6256	$250.63	$250.65	$250.60
7 purchase totals =	$926.60		$993.3149	$993.33	$993.35	$993.10