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	$183.26	4.572%	$191.6386	$191.64	$191.65	$191.60
Purchase #2	$84.46	7.278%	$90.607	$90.61	$90.60	$90.60
Purchase #3	$76.75	12.754%	$86.5387	$86.54	$86.55	$86.50
Purchase #4	$77.33	4.478%	$80.7928	$80.79	$80.80	$80.80
Purchase #5	$165.30	11.399%	$184.1425	$184.14	$184.15	$184.10
Purchase #6	$121.87	5.759%	$128.8885	$128.89	$128.90	$128.90
Purchase #7	$57.84	12.595%	$65.1249	$65.12	$65.10	$65.10
7 purchase totals =	$766.81		$827.7330	$827.73	$827.75	$827.60