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	$120.27	13.837%	$136.9118	$136.91	$136.90	$136.90
Purchase #2	$222.33	11.674%	$248.2848	$248.28	$248.30	$248.30
Purchase #3	$50.46	11.165%	$56.0939	$56.09	$56.10	$56.10
Purchase #4	$164.34	3.283%	$169.7353	$169.74	$169.75	$169.70
Purchase #5	$71.98	9.479%	$78.803	$78.80	$78.80	$78.80
Purchase #6	$175.25	8.781%	$190.6387	$190.64	$190.65	$190.60
Purchase #7	$72.66	11.341%	$80.9004	$80.90	$80.90	$80.90
7 purchase totals =	$877.29		$961.3679	$961.36	$961.40	$961.30