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	$100.40	13.555%	$114.0092	$114.01	$114.00	$114.00
Purchase #2	$246.72	7.534%	$265.3079	$265.31	$265.30	$265.30
Purchase #3	$80.88	11.618%	$90.2766	$90.28	$90.30	$90.30
Purchase #4	$143.85	10.685%	$159.2204	$159.22	$159.20	$159.20
Purchase #5	$31.98	3.516%	$33.1044	$33.10	$33.10	$33.10
Purchase #6	$83.59	9.538%	$91.5628	$91.56	$91.55	$91.60
Purchase #7	$240.39	11.441%	$267.893	$267.89	$267.90	$267.90
7 purchase totals =	$927.81		$1,021.3743	$1,021.37	$1,021.35	$1,021.40