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	$205.48	11.477%	$229.0629	$229.06	$229.05	$229.10
Purchase #2	$238.75	13.102%	$270.031	$270.03	$270.05	$270.00
Purchase #3	$145.46	11.638%	$162.3886	$162.39	$162.40	$162.40
Purchase #4	$196.71	7.557%	$211.5754	$211.58	$211.60	$211.60
Purchase #5	$63.39	5.713%	$67.0115	$67.01	$67.00	$67.00
Purchase #6	$176.88	11.226%	$196.7365	$196.74	$196.75	$196.70
Purchase #7	$141.28	8.230%	$152.9073	$152.91	$152.90	$152.90
7 purchase totals =	$1,167.95		$1,289.7132	$1,289.72	$1,289.75	$1,289.70