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	$58.35	12.170%	$65.4512	$65.45	$65.45	$65.50
Purchase #2	$226.91	10.487%	$250.7061	$250.71	$250.70	$250.70
Purchase #3	$249.30	6.227%	$264.8239	$264.82	$264.80	$264.80
Purchase #4	$98.94	6.165%	$105.0397	$105.04	$105.05	$105.00
Purchase #5	$125.80	11.609%	$140.4041	$140.40	$140.40	$140.40
Purchase #6	$63.59	5.680%	$67.2019	$67.20	$67.20	$67.20
Purchase #7	$203.76	6.774%	$217.5627	$217.56	$217.55	$217.60
7 purchase totals =	$1,026.65		$1,111.1896	$1,111.18	$1,111.15	$1,111.20