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	$238.37	12.809%	$268.9028	$268.90	$268.90	$268.90
Purchase #2	$83.90	10.741%	$92.9117	$92.91	$92.90	$92.90
Purchase #3	$26.25	6.138%	$27.8612	$27.86	$27.85	$27.90
Purchase #4	$222.63	5.285%	$234.396	$234.40	$234.40	$234.40
Purchase #5	$245.26	7.807%	$264.4074	$264.41	$264.40	$264.40
Purchase #6	$18.53	10.643%	$20.5021	$20.50	$20.50	$20.50
Purchase #7	$21.95	3.148%	$22.641	$22.64	$22.65	$22.60
7 purchase totals =	$856.89		$931.6222	$931.62	$931.60	$931.60