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	$165.56	8.652%	$179.8843	$179.88	$179.90	$179.90
Purchase #2	$148.46	5.659%	$156.8614	$156.86	$156.85	$156.90
Purchase #3	$228.63	8.465%	$247.9835	$247.98	$248.00	$248.00
Purchase #4	$171.29	4.424%	$178.8679	$178.87	$178.85	$178.90
Purchase #5	$59.84	10.788%	$66.2955	$66.30	$66.30	$66.30
Purchase #6	$90.66	11.441%	$101.0324	$101.03	$101.05	$101.00
Purchase #7	$240.28	4.423%	$250.9076	$250.91	$250.90	$250.90
7 purchase totals =	$1,104.72		$1,181.8326	$1,181.83	$1,181.85	$1,181.90