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	$178.94	6.603%	$190.7554	$190.76	$190.75	$190.80
Purchase #2	$37.87	13.176%	$42.8598	$42.86	$42.85	$42.90
Purchase #3	$30.55	6.122%	$32.4203	$32.42	$32.40	$32.40
Purchase #4	$98.53	11.359%	$109.722	$109.72	$109.70	$109.70
Purchase #5	$79.87	13.266%	$90.4656	$90.47	$90.45	$90.50
Purchase #6	$81.38	8.729%	$88.4837	$88.48	$88.50	$88.50
Purchase #7	$85.56	8.580%	$92.901	$92.90	$92.90	$92.90
7 purchase totals =	$592.70		$647.6078	$647.61	$647.55	$647.70