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	$120.73	13.280%	$136.7629	$136.76	$136.75	$136.80
Purchase #2	$38.80	10.672%	$42.9407	$42.94	$42.95	$42.90
Purchase #3	$44.75	12.846%	$50.4986	$50.50	$50.50	$50.50
Purchase #4	$213.84	7.520%	$229.9208	$229.92	$229.90	$229.90
Purchase #5	$165.38	13.786%	$188.1793	$188.18	$188.20	$188.20
Purchase #6	$118.56	7.717%	$127.7093	$127.71	$127.70	$127.70
Purchase #7	$67.95	4.854%	$71.2483	$71.25	$71.25	$71.20
7 purchase totals =	$770.01		$847.2599	$847.26	$847.25	$847.20