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	$85.67	5.618%	$90.4829	$90.48	$90.50	$90.50
Purchase #2	$65.27	9.611%	$71.5431	$71.54	$71.55	$71.50
Purchase #3	$117.41	7.134%	$125.786	$125.79	$125.80	$125.80
Purchase #4	$25.62	9.833%	$28.1392	$28.14	$28.15	$28.10
Purchase #5	$162.96	4.373%	$170.0862	$170.09	$170.10	$170.10
Purchase #6	$208.69	4.176%	$217.4049	$217.40	$217.40	$217.40
Purchase #7	$85.33	4.304%	$89.0026	$89.00	$89.00	$89.00
7 purchase totals =	$750.95		$792.4449	$792.44	$792.50	$792.40