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	$88.48	11.812%	$98.9313	$98.93	$98.95	$98.90
Purchase #2	$46.97	6.718%	$50.1254	$50.13	$50.15	$50.10
Purchase #3	$82.76	8.405%	$89.716	$89.72	$89.70	$89.70
Purchase #4	$149.96	8.380%	$162.5266	$162.53	$162.55	$162.50
Purchase #5	$145.83	10.103%	$160.5632	$160.56	$160.55	$160.60
Purchase #6	$63.33	5.209%	$66.6289	$66.63	$66.65	$66.60
Purchase #7	$212.45	7.562%	$228.5155	$228.52	$228.50	$228.50
7 purchase totals =	$789.78		$857.0069	$857.02	$857.05	$856.90