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	$135.47	10.839%	$150.1536	$150.15	$150.15	$150.20
Purchase #2	$211.38	5.171%	$222.3105	$222.31	$222.30	$222.30
Purchase #3	$231.88	12.468%	$260.7908	$260.79	$260.80	$260.80
Purchase #4	$152.69	3.399%	$157.8799	$157.88	$157.90	$157.90
Purchase #5	$153.57	12.122%	$172.1858	$172.19	$172.20	$172.20
Purchase #6	$67.34	8.300%	$72.9292	$72.93	$72.95	$72.90
Purchase #7	$75.39	8.198%	$81.5705	$81.57	$81.55	$81.60
7 purchase totals =	$1,027.72		$1,117.8203	$1,117.82	$1,117.85	$1,117.90