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	$78.83	3.398%	$81.5086	$81.51	$81.50	$81.50
Purchase #2	$113.53	10.271%	$125.1907	$125.19	$125.20	$125.20
Purchase #3	$61.57	7.806%	$66.3762	$66.38	$66.40	$66.40
Purchase #4	$250.81	12.562%	$282.3168	$282.32	$282.30	$282.30
Purchase #5	$67.58	6.199%	$71.7693	$71.77	$71.75	$71.80
Purchase #6	$111.80	8.147%	$120.9083	$120.91	$120.90	$120.90
Purchase #7	$79.71	12.527%	$89.6953	$89.70	$89.70	$89.70
7 purchase totals =	$763.83		$837.7652	$837.78	$837.75	$837.80