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	$227.43	10.362%	$250.9963	$251.00	$251.00	$251.00
Purchase #2	$166.98	13.384%	$189.3286	$189.33	$189.35	$189.30
Purchase #3	$87.86	4.573%	$91.8778	$91.88	$91.90	$91.90
Purchase #4	$99.43	6.382%	$105.7756	$105.78	$105.80	$105.80
Purchase #5	$57.82	8.824%	$62.922	$62.92	$62.90	$62.90
Purchase #6	$115.57	7.281%	$123.9847	$123.98	$124.00	$124.00
Purchase #7	$90.77	11.661%	$101.3547	$101.35	$101.35	$101.40
7 purchase totals =	$845.86		$926.2397	$926.24	$926.30	$926.30