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	$93.83	6.320%	$99.7601	$99.76	$99.75	$99.80
Purchase #2	$30.55	11.166%	$33.9612	$33.96	$33.95	$34.00
Purchase #3	$25.71	9.790%	$28.227	$28.23	$28.25	$28.20
Purchase #4	$186.34	12.472%	$209.5803	$209.58	$209.60	$209.60
Purchase #5	$38.48	11.520%	$42.9129	$42.91	$42.90	$42.90
Purchase #6	$115.98	12.808%	$130.8347	$130.83	$130.85	$130.80
Purchase #7	$99.40	11.824%	$111.1531	$111.15	$111.15	$111.20
7 purchase totals =	$590.29		$656.4293	$656.42	$656.45	$656.50