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	$128.37	10.449%	$141.7834	$141.78	$141.80	$141.80
Purchase #2	$6.82	6.761%	$7.2811	$7.28	$7.30	$7.30
Purchase #3	$231.74	7.681%	$249.5399	$249.54	$249.55	$249.50
Purchase #4	$138.83	6.560%	$147.9372	$147.94	$147.95	$147.90
Purchase #5	$93.50	12.784%	$105.453	$105.45	$105.45	$105.50
Purchase #6	$85.89	9.827%	$94.3304	$94.33	$94.35	$94.30
Purchase #7	$110.90	12.763%	$125.0542	$125.05	$125.05	$125.10
7 purchase totals =	$796.05		$871.3792	$871.37	$871.45	$871.40