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	$182.83	3.387%	$189.0225	$189.02	$189.00	$189.00
Purchase #2	$191.33	4.473%	$199.8882	$199.89	$199.90	$199.90
Purchase #3	$207.27	7.734%	$223.3003	$223.30	$223.30	$223.30
Purchase #4	$18.88	8.806%	$20.5426	$20.54	$20.55	$20.50
Purchase #5	$181.61	7.822%	$195.8155	$195.82	$195.80	$195.80
Purchase #6	$127.83	13.549%	$145.1497	$145.15	$145.15	$145.10
Purchase #7	$147.36	4.669%	$154.2402	$154.24	$154.25	$154.20
7 purchase totals =	$1,057.11		$1,127.9590	$1,127.96	$1,127.95	$1,127.80