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	$110.92	12.270%	$124.5299	$124.53	$124.55	$124.50
Purchase #2	$101.74	3.104%	$104.898	$104.90	$104.90	$104.90
Purchase #3	$96.38	13.214%	$109.1157	$109.12	$109.10	$109.10
Purchase #4	$139.28	5.471%	$146.9	$146.90	$146.90	$146.90
Purchase #5	$165.95	6.290%	$176.3883	$176.39	$176.40	$176.40
Purchase #6	$136.63	4.358%	$142.5843	$142.58	$142.60	$142.60
Purchase #7	$121.73	5.521%	$128.4507	$128.45	$128.45	$128.50
7 purchase totals =	$872.63		$932.8669	$932.87	$932.90	$932.90