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	$179.40	3.418%	$185.5319	$185.53	$185.55	$185.50
Purchase #2	$131.50	4.365%	$137.24	$137.24	$137.25	$137.20
Purchase #3	$40.91	4.834%	$42.8876	$42.89	$42.90	$42.90
Purchase #4	$85.54	13.287%	$96.9057	$96.91	$96.90	$96.90
Purchase #5	$207.56	7.542%	$223.2142	$223.21	$223.20	$223.20
Purchase #6	$19.28	9.223%	$21.0582	$21.06	$21.05	$21.10
Purchase #7	$207.34	5.623%	$218.9987	$219.00	$219.00	$219.00
7 purchase totals =	$871.53		$925.8363	$925.84	$925.85	$925.80