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	$81.49	6.326%	$86.6451	$86.65	$86.65	$86.60
Purchase #2	$55.76	12.839%	$62.919	$62.92	$62.90	$62.90
Purchase #3	$130.82	8.121%	$141.4439	$141.44	$141.45	$141.40
Purchase #4	$248.27	11.135%	$275.9149	$275.91	$275.90	$275.90
Purchase #5	$250.90	9.226%	$274.048	$274.05	$274.05	$274.00
Purchase #6	$219.45	8.826%	$238.8187	$238.82	$238.80	$238.80
Purchase #7	$131.80	11.797%	$147.3484	$147.35	$147.35	$147.30
7 purchase totals =	$1,118.49		$1,227.1380	$1,227.14	$1,227.10	$1,226.90