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	$91.32	10.132%	$100.5725	$100.57	$100.55	$100.60
Purchase #2	$63.27	6.331%	$67.2756	$67.28	$67.30	$67.30
Purchase #3	$112.25	11.771%	$125.4629	$125.46	$125.45	$125.50
Purchase #4	$35.86	7.250%	$38.4599	$38.46	$38.45	$38.50
Purchase #5	$53.98	3.112%	$55.6599	$55.66	$55.65	$55.70
Purchase #6	$159.89	4.705%	$167.4128	$167.41	$167.40	$167.40
Purchase #7	$234.91	4.247%	$244.8866	$244.89	$244.90	$244.90
7 purchase totals =	$751.48		$799.7302	$799.73	$799.70	$799.90