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	$74.56	10.287%	$82.23	$82.23	$82.25	$82.20
Purchase #2	$166.31	12.675%	$187.3898	$187.39	$187.40	$187.40
Purchase #3	$80.27	13.624%	$91.206	$91.21	$91.20	$91.20
Purchase #4	$250.57	4.231%	$261.1716	$261.17	$261.15	$261.20
Purchase #5	$229.89	4.555%	$240.3615	$240.36	$240.35	$240.40
Purchase #6	$6.65	9.303%	$7.2686	$7.27	$7.25	$7.30
Purchase #7	$180.29	6.836%	$192.6146	$192.61	$192.60	$192.60
7 purchase totals =	$988.54		$1,062.2421	$1,062.24	$1,062.20	$1,062.30