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	$171.41	3.665%	$177.6922	$177.69	$177.70	$177.70
Purchase #2	$31.37	11.520%	$34.9838	$34.98	$35.00	$35.00
Purchase #3	$60.89	3.334%	$62.9201	$62.92	$62.90	$62.90
Purchase #4	$84.87	5.267%	$89.3401	$89.34	$89.35	$89.30
Purchase #5	$52.56	10.199%	$57.9206	$57.92	$57.90	$57.90
Purchase #6	$216.89	8.419%	$235.15	$235.15	$235.15	$235.20
Purchase #7	$185.90	5.523%	$196.1673	$196.17	$196.15	$196.20
7 purchase totals =	$803.89		$854.1741	$854.17	$854.15	$854.20