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	$37.74	12.372%	$42.4092	$42.41	$42.40	$42.40
Purchase #2	$6.95	12.548%	$7.8221	$7.82	$7.80	$7.80
Purchase #3	$193.90	6.774%	$207.0348	$207.03	$207.05	$207.00
Purchase #4	$239.52	5.777%	$253.3571	$253.36	$253.35	$253.40
Purchase #5	$179.37	11.213%	$199.4828	$199.48	$199.50	$199.50
Purchase #6	$216.35	12.273%	$242.9026	$242.90	$242.90	$242.90
Purchase #7	$104.47	8.689%	$113.5474	$113.55	$113.55	$113.50
7 purchase totals =	$978.30		$1,066.5560	$1,066.55	$1,066.55	$1,066.50