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	$216.86	7.618%	$233.3804	$233.38	$233.40	$233.40
Purchase #2	$157.79	3.226%	$162.8803	$162.88	$162.90	$162.90
Purchase #3	$209.50	6.456%	$223.0253	$223.03	$223.05	$223.00
Purchase #4	$99.33	11.493%	$110.746	$110.75	$110.75	$110.70
Purchase #5	$101.52	4.141%	$105.7239	$105.72	$105.70	$105.70
Purchase #6	$101.32	7.112%	$108.5259	$108.53	$108.55	$108.50
Purchase #7	$30.86	9.651%	$33.8383	$33.84	$33.85	$33.80
7 purchase totals =	$917.18		$978.1201	$978.13	$978.20	$978.00