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	$75.79	4.538%	$79.2294	$79.23	$79.25	$79.20
Purchase #2	$90.34	12.546%	$101.6741	$101.67	$101.65	$101.70
Purchase #3	$94.61	10.626%	$104.6633	$104.66	$104.65	$104.70
Purchase #4	$212.64	7.303%	$228.1691	$228.17	$228.15	$228.20
Purchase #5	$88.61	3.357%	$91.5846	$91.58	$91.60	$91.60
Purchase #6	$156.72	9.499%	$171.6068	$171.61	$171.60	$171.60
Purchase #7	$39.59	9.442%	$43.3281	$43.33	$43.35	$43.30
7 purchase totals =	$758.30		$820.2554	$820.25	$820.25	$820.30