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	$124.71	5.277%	$131.2909	$131.29	$131.30	$131.30
Purchase #2	$100.84	8.821%	$109.7351	$109.74	$109.75	$109.70
Purchase #3	$235.37	10.350%	$259.7308	$259.73	$259.75	$259.70
Purchase #4	$27.89	11.579%	$31.1194	$31.12	$31.10	$31.10
Purchase #5	$95.38	13.559%	$108.3126	$108.31	$108.30	$108.30
Purchase #6	$89.85	11.663%	$100.3292	$100.33	$100.35	$100.30
Purchase #7	$96.56	8.463%	$104.7319	$104.73	$104.75	$104.70
7 purchase totals =	$770.60		$845.2499	$845.25	$845.30	$845.10