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	$84.91	6.379%	$90.3264	$90.33	$90.35	$90.30
Purchase #2	$174.80	5.434%	$184.2986	$184.30	$184.30	$184.30
Purchase #3	$184.50	5.371%	$194.4095	$194.41	$194.40	$194.40
Purchase #4	$71.91	9.438%	$78.6969	$78.70	$78.70	$78.70
Purchase #5	$6.93	13.836%	$7.8888	$7.89	$7.90	$7.90
Purchase #6	$90.41	11.636%	$100.9301	$100.93	$100.95	$100.90
Purchase #7	$227.98	11.112%	$253.3131	$253.31	$253.30	$253.30
7 purchase totals =	$841.44		$909.8634	$909.87	$909.90	$909.80