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	$119.28	7.460%	$128.1783	$128.18	$128.20	$128.20
Purchase #2	$93.65	12.356%	$105.2214	$105.22	$105.20	$105.20
Purchase #3	$139.75	12.745%	$157.5611	$157.56	$157.55	$157.60
Purchase #4	$186.87	10.191%	$205.9139	$205.91	$205.90	$205.90
Purchase #5	$45.99	7.437%	$49.4103	$49.41	$49.40	$49.40
Purchase #6	$239.41	10.590%	$264.7635	$264.76	$264.75	$264.80
Purchase #7	$90.91	9.803%	$99.8219	$99.82	$99.80	$99.80
7 purchase totals =	$915.86		$1,010.8704	$1,010.86	$1,010.80	$1,010.90