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	$244.37	11.796%	$273.1959	$273.20	$273.20	$273.20
Purchase #2	$28.45	11.304%	$31.666	$31.67	$31.65	$31.70
Purchase #3	$178.96	8.179%	$193.5971	$193.60	$193.60	$193.60
Purchase #4	$30.36	6.860%	$32.4427	$32.44	$32.45	$32.40
Purchase #5	$110.59	11.415%	$123.2138	$123.21	$123.20	$123.20
Purchase #6	$85.25	6.282%	$90.6054	$90.61	$90.60	$90.60
Purchase #7	$222.87	4.601%	$233.1242	$233.12	$233.10	$233.10
7 purchase totals =	$900.85		$977.8451	$977.85	$977.80	$977.80