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	$53.89	8.358%	$58.3941	$58.39	$58.40	$58.40
Purchase #2	$93.54	10.503%	$103.3645	$103.36	$103.35	$103.40
Purchase #3	$82.55	6.440%	$87.8662	$87.87	$87.85	$87.90
Purchase #4	$50.65	11.874%	$56.6642	$56.66	$56.65	$56.70
Purchase #5	$91.35	9.219%	$99.7716	$99.77	$99.75	$99.80
Purchase #6	$220.44	10.614%	$243.8375	$243.84	$243.85	$243.80
Purchase #7	$74.25	6.223%	$78.8706	$78.87	$78.85	$78.90
7 purchase totals =	$666.67		$728.7687	$728.76	$728.70	$728.90