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	$35.59	5.555%	$37.567	$37.57	$37.55	$37.60
Purchase #2	$222.30	12.656%	$250.4343	$250.43	$250.45	$250.40
Purchase #3	$219.42	7.869%	$236.6862	$236.69	$236.70	$236.70
Purchase #4	$192.26	4.819%	$201.525	$201.53	$201.55	$201.50
Purchase #5	$17.46	10.851%	$19.3546	$19.35	$19.35	$19.40
Purchase #6	$180.82	8.668%	$196.4935	$196.49	$196.50	$196.50
Purchase #7	$37.33	13.124%	$42.2292	$42.23	$42.25	$42.20
7 purchase totals =	$905.18		$984.2898	$984.29	$984.35	$984.30