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	$201.28	8.495%	$218.3787	$218.38	$218.40	$218.40
Purchase #2	$133.25	5.489%	$140.5641	$140.56	$140.55	$140.60
Purchase #3	$147.56	12.415%	$165.8796	$165.88	$165.90	$165.90
Purchase #4	$219.83	10.259%	$242.3824	$242.38	$242.40	$242.40
Purchase #5	$157.42	13.772%	$179.0999	$179.10	$179.10	$179.10
Purchase #6	$69.61	3.610%	$72.1229	$72.12	$72.10	$72.10
Purchase #7	$172.71	4.654%	$180.7479	$180.75	$180.75	$180.70
7 purchase totals =	$1,101.66		$1,199.1755	$1,199.17	$1,199.20	$1,199.20