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	$213.55	4.824%	$223.8517	$223.85	$223.85	$223.90
Purchase #2	$195.82	12.283%	$219.8726	$219.87	$219.85	$219.90
Purchase #3	$97.35	12.311%	$109.3348	$109.33	$109.35	$109.30
Purchase #4	$83.42	7.758%	$89.8917	$89.89	$89.90	$89.90
Purchase #5	$168.63	13.289%	$191.0392	$191.04	$191.05	$191.00
Purchase #6	$247.43	13.120%	$279.8928	$279.89	$279.90	$279.90
Purchase #7	$114.61	13.129%	$129.6571	$129.66	$129.65	$129.70
7 purchase totals =	$1,120.81		$1,243.5399	$1,243.53	$1,243.55	$1,243.60