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	$91.84	12.130%	$102.9802	$102.98	$103.00	$103.00
Purchase #2	$91.30	12.299%	$102.529	$102.53	$102.55	$102.50
Purchase #3	$126.55	3.758%	$131.3057	$131.31	$131.30	$131.30
Purchase #4	$124.27	10.385%	$137.1754	$137.18	$137.20	$137.20
Purchase #5	$137.59	9.207%	$150.2579	$150.26	$150.25	$150.30
Purchase #6	$82.98	11.447%	$92.4787	$92.48	$92.50	$92.50
Purchase #7	$179.74	6.814%	$191.9875	$191.99	$192.00	$192.00
7 purchase totals =	$834.27		$908.7144	$908.73	$908.80	$908.80