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	$18.44	5.280%	$19.4136	$19.41	$19.40	$19.40
Purchase #2	$39.80	6.862%	$42.5311	$42.53	$42.55	$42.50
Purchase #3	$209.27	3.644%	$216.8958	$216.90	$216.90	$216.90
Purchase #4	$212.91	3.502%	$220.3661	$220.37	$220.35	$220.40
Purchase #5	$178.27	7.326%	$191.3301	$191.33	$191.35	$191.30
Purchase #6	$92.76	8.226%	$100.3904	$100.39	$100.40	$100.40
Purchase #7	$54.81	8.131%	$59.2666	$59.27	$59.25	$59.30
7 purchase totals =	$806.26		$850.1937	$850.20	$850.20	$850.20