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	$37.33	12.630%	$42.0448	$42.04	$42.05	$42.00
Purchase #2	$71.40	10.190%	$78.6757	$78.68	$78.70	$78.70
Purchase #3	$67.39	3.346%	$69.6449	$69.64	$69.65	$69.60
Purchase #4	$86.48	3.387%	$89.4091	$89.41	$89.40	$89.40
Purchase #5	$234.71	4.581%	$245.4621	$245.46	$245.45	$245.50
Purchase #6	$207.94	7.774%	$224.1053	$224.11	$224.10	$224.10
Purchase #7	$205.72	3.241%	$212.3874	$212.39	$212.40	$212.40
7 purchase totals =	$910.97		$961.7293	$961.73	$961.75	$961.70