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	$8.57	7.125%	$9.1806	$9.18	$9.20	$9.20
Purchase #2	$149.78	3.665%	$155.2694	$155.27	$155.25	$155.30
Purchase #3	$142.96	8.124%	$154.5741	$154.57	$154.55	$154.60
Purchase #4	$39.89	8.793%	$43.3975	$43.40	$43.40	$43.40
Purchase #5	$209.64	4.130%	$218.2981	$218.30	$218.30	$218.30
Purchase #6	$243.34	6.148%	$258.3005	$258.30	$258.30	$258.30
Purchase #7	$154.88	6.185%	$164.4593	$164.46	$164.45	$164.50
7 purchase totals =	$949.06		$1,003.4795	$1,003.48	$1,003.45	$1,003.60