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	$74.66	7.640%	$80.364	$80.36	$80.35	$80.40
Purchase #2	$109.63	3.545%	$113.5164	$113.52	$113.50	$113.50
Purchase #3	$24.68	10.362%	$27.2373	$27.24	$27.25	$27.20
Purchase #4	$38.40	4.598%	$40.1656	$40.17	$40.15	$40.20
Purchase #5	$86.34	12.165%	$96.8433	$96.84	$96.85	$96.80
Purchase #6	$202.48	3.344%	$209.2509	$209.25	$209.25	$209.30
Purchase #7	$90.87	6.223%	$96.5248	$96.52	$96.50	$96.50
7 purchase totals =	$627.06		$663.9023	$663.90	$663.85	$663.90