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	$83.90	9.457%	$91.8344	$91.83	$91.85	$91.80
Purchase #2	$23.64	13.180%	$26.7558	$26.76	$26.75	$26.80
Purchase #3	$142.77	6.695%	$152.3285	$152.33	$152.35	$152.30
Purchase #4	$131.37	9.354%	$143.6583	$143.66	$143.65	$143.70
Purchase #5	$178.42	7.355%	$191.5428	$191.54	$191.55	$191.50
Purchase #6	$123.74	3.764%	$128.3976	$128.40	$128.40	$128.40
Purchase #7	$80.46	12.248%	$90.3147	$90.31	$90.30	$90.30
7 purchase totals =	$764.30		$824.8321	$824.83	$824.85	$824.80