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	$5.98	12.799%	$6.7454	$6.75	$6.75	$6.70
Purchase #2	$221.43	7.575%	$238.2033	$238.20	$238.20	$238.20
Purchase #3	$78.69	6.481%	$83.7899	$83.79	$83.80	$83.80
Purchase #4	$189.95	3.651%	$196.8851	$196.89	$196.90	$196.90
Purchase #5	$73.81	5.357%	$77.764	$77.76	$77.75	$77.80
Purchase #6	$26.82	3.793%	$27.8373	$27.84	$27.85	$27.80
Purchase #7	$92.91	7.782%	$100.1403	$100.14	$100.15	$100.10
7 purchase totals =	$689.59		$731.3653	$731.37	$731.40	$731.30