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	$180.76	3.104%	$186.3708	$186.37	$186.35	$186.40
Purchase #2	$154.25	13.380%	$174.8887	$174.89	$174.90	$174.90
Purchase #3	$50.49	9.276%	$55.1735	$55.17	$55.15	$55.20
Purchase #4	$177.39	7.676%	$191.0065	$191.01	$191.00	$191.00
Purchase #5	$17.84	3.310%	$18.4305	$18.43	$18.45	$18.40
Purchase #6	$234.95	10.410%	$259.4083	$259.41	$259.40	$259.40
Purchase #7	$71.74	9.731%	$78.721	$78.72	$78.70	$78.70
7 purchase totals =	$887.42		$963.9993	$964.00	$963.95	$964.00