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	$77.64	13.844%	$88.3885	$88.39	$88.40	$88.40
Purchase #2	$203.73	12.812%	$229.8319	$229.83	$229.85	$229.80
Purchase #3	$250.96	9.368%	$274.4699	$274.47	$274.45	$274.50
Purchase #4	$92.27	6.591%	$98.3515	$98.35	$98.35	$98.40
Purchase #5	$41.86	9.714%	$45.9263	$45.93	$45.95	$45.90
Purchase #6	$249.58	3.814%	$259.099	$259.10	$259.10	$259.10
Purchase #7	$170.61	11.570%	$190.3496	$190.35	$190.35	$190.30
7 purchase totals =	$1,086.65		$1,186.4167	$1,186.42	$1,186.45	$1,186.40