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	$9.71	6.115%	$10.3038	$10.30	$10.30	$10.30
Purchase #2	$40.78	10.828%	$45.1957	$45.20	$45.20	$45.20
Purchase #3	$224.33	4.597%	$234.6425	$234.64	$234.65	$234.60
Purchase #4	$153.26	9.544%	$167.8871	$167.89	$167.90	$167.90
Purchase #5	$174.56	12.459%	$196.3084	$196.31	$196.30	$196.30
Purchase #6	$70.38	13.281%	$79.7272	$79.73	$79.75	$79.70
Purchase #7	$169.71	12.663%	$191.2004	$191.20	$191.20	$191.20
7 purchase totals =	$842.73		$925.2651	$925.27	$925.30	$925.20