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	$73.90	6.815%	$78.9363	$78.94	$78.95	$78.90
Purchase #2	$6.33	12.418%	$7.1161	$7.12	$7.10	$7.10
Purchase #3	$75.30	3.263%	$77.757	$77.76	$77.75	$77.80
Purchase #4	$215.61	3.163%	$222.4297	$222.43	$222.45	$222.40
Purchase #5	$189.52	11.473%	$211.2636	$211.26	$211.25	$211.30
Purchase #6	$18.57	11.386%	$20.6844	$20.68	$20.70	$20.70
Purchase #7	$132.57	5.219%	$139.4888	$139.49	$139.50	$139.50
7 purchase totals =	$711.80		$757.6759	$757.68	$757.70	$757.70