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	$245.85	9.854%	$270.0761	$270.08	$270.10	$270.10
Purchase #2	$170.30	13.783%	$193.7724	$193.77	$193.75	$193.80
Purchase #3	$161.34	6.471%	$171.7803	$171.78	$171.80	$171.80
Purchase #4	$79.85	12.628%	$89.9335	$89.93	$89.95	$89.90
Purchase #5	$39.44	9.736%	$43.2799	$43.28	$43.30	$43.30
Purchase #6	$33.46	11.848%	$37.4243	$37.42	$37.40	$37.40
Purchase #7	$64.57	3.817%	$67.0346	$67.03	$67.05	$67.00
7 purchase totals =	$794.81		$873.3011	$873.29	$873.35	$873.30