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	$186.96	6.301%	$198.7403	$198.74	$198.75	$198.70
Purchase #2	$20.76	4.701%	$21.7359	$21.74	$21.75	$21.70
Purchase #3	$224.44	4.214%	$233.8979	$233.90	$233.90	$233.90
Purchase #4	$171.62	10.295%	$189.2883	$189.29	$189.30	$189.30
Purchase #5	$67.29	6.838%	$71.8913	$71.89	$71.90	$71.90
Purchase #6	$223.73	11.459%	$249.3672	$249.37	$249.35	$249.40
Purchase #7	$129.85	8.105%	$140.3743	$140.37	$140.35	$140.40
7 purchase totals =	$1,024.65		$1,105.2952	$1,105.30	$1,105.30	$1,105.30