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	$154.61	13.379%	$175.2953	$175.30	$175.30	$175.30
Purchase #2	$45.73	7.303%	$49.0697	$49.07	$49.05	$49.10
Purchase #3	$84.31	6.574%	$89.8525	$89.85	$89.85	$89.90
Purchase #4	$73.91	9.199%	$80.709	$80.71	$80.70	$80.70
Purchase #5	$52.89	8.275%	$57.2666	$57.27	$57.25	$57.30
Purchase #6	$143.70	8.489%	$155.8987	$155.90	$155.90	$155.90
Purchase #7	$198.67	9.407%	$217.3589	$217.36	$217.35	$217.40
7 purchase totals =	$753.82		$825.4507	$825.46	$825.40	$825.60