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	$249.35	11.802%	$278.7783	$278.78	$278.80	$278.80
Purchase #2	$212.88	5.828%	$225.2866	$225.29	$225.30	$225.30
Purchase #3	$38.40	3.648%	$39.8008	$39.80	$39.80	$39.80
Purchase #4	$18.63	9.109%	$20.327	$20.33	$20.35	$20.30
Purchase #5	$41.35	6.162%	$43.898	$43.90	$43.90	$43.90
Purchase #6	$209.34	3.375%	$216.4052	$216.41	$216.40	$216.40
Purchase #7	$235.70	9.439%	$257.9477	$257.95	$257.95	$257.90
7 purchase totals =	$1,005.65		$1,082.4436	$1,082.46	$1,082.50	$1,082.40