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	$190.90	4.642%	$199.7616	$199.76	$199.75	$199.80
Purchase #2	$190.88	9.448%	$208.9143	$208.91	$208.90	$208.90
Purchase #3	$169.82	13.523%	$192.7848	$192.78	$192.80	$192.80
Purchase #4	$96.69	3.760%	$100.3255	$100.33	$100.35	$100.30
Purchase #5	$243.38	9.218%	$265.8148	$265.81	$265.80	$265.80
Purchase #6	$57.36	12.845%	$64.7279	$64.73	$64.75	$64.70
Purchase #7	$6.50	4.869%	$6.8165	$6.82	$6.80	$6.80
7 purchase totals =	$955.53		$1,039.1454	$1,039.14	$1,039.15	$1,039.10