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	$186.80	6.393%	$198.7421	$198.74	$198.75	$198.70
Purchase #2	$110.65	11.865%	$123.7786	$123.78	$123.80	$123.80
Purchase #3	$220.97	12.801%	$249.2564	$249.26	$249.25	$249.30
Purchase #4	$56.54	11.108%	$62.8205	$62.82	$62.80	$62.80
Purchase #5	$103.56	12.155%	$116.1477	$116.15	$116.15	$116.10
Purchase #6	$181.40	5.424%	$191.2391	$191.24	$191.25	$191.20
Purchase #7	$240.66	12.160%	$269.9243	$269.92	$269.90	$269.90
7 purchase totals =	$1,100.58		$1,211.9087	$1,211.91	$1,211.90	$1,211.80