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	$171.27	11.858%	$191.5792	$191.58	$191.60	$191.60
Purchase #2	$26.57	12.581%	$29.9128	$29.91	$29.90	$29.90
Purchase #3	$200.46	11.575%	$223.6632	$223.66	$223.65	$223.70
Purchase #4	$27.72	13.273%	$31.3993	$31.40	$31.40	$31.40
Purchase #5	$209.86	10.615%	$232.1366	$232.14	$232.15	$232.10
Purchase #6	$159.30	7.586%	$171.3845	$171.38	$171.40	$171.40
Purchase #7	$64.42	9.151%	$70.3151	$70.32	$70.30	$70.30
7 purchase totals =	$859.60		$950.3907	$950.39	$950.40	$950.40