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	$86.39	3.447%	$89.3679	$89.37	$89.35	$89.40
Purchase #2	$43.51	11.260%	$48.4092	$48.41	$48.40	$48.40
Purchase #3	$233.55	4.410%	$243.8496	$243.85	$243.85	$243.80
Purchase #4	$157.96	7.572%	$169.9207	$169.92	$169.90	$169.90
Purchase #5	$159.41	10.225%	$175.7097	$175.71	$175.70	$175.70
Purchase #6	$210.34	8.687%	$228.6122	$228.61	$228.60	$228.60
Purchase #7	$124.28	10.165%	$136.9131	$136.91	$136.90	$136.90
7 purchase totals =	$1,015.44		$1,092.7824	$1,092.78	$1,092.70	$1,092.70