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	$204.88	12.121%	$229.7135	$229.71	$229.70	$229.70
Purchase #2	$81.26	10.474%	$89.7712	$89.77	$89.75	$89.80
Purchase #3	$27.98	12.417%	$31.4543	$31.45	$31.45	$31.50
Purchase #4	$218.27	10.244%	$240.6296	$240.63	$240.65	$240.60
Purchase #5	$123.31	12.736%	$139.0148	$139.01	$139.00	$139.00
Purchase #6	$79.64	13.698%	$90.5491	$90.55	$90.55	$90.50
Purchase #7	$31.29	3.519%	$32.3911	$32.39	$32.40	$32.40
7 purchase totals =	$766.63		$853.5236	$853.51	$853.50	$853.50