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	$62.64	8.426%	$67.918	$67.92	$67.90	$67.90
Purchase #2	$202.50	12.204%	$227.2131	$227.21	$227.20	$227.20
Purchase #3	$85.33	5.223%	$89.7868	$89.79	$89.80	$89.80
Purchase #4	$210.35	6.755%	$224.5591	$224.56	$224.55	$224.60
Purchase #5	$161.85	10.630%	$179.0547	$179.05	$179.05	$179.10
Purchase #6	$70.44	4.212%	$73.4069	$73.41	$73.40	$73.40
Purchase #7	$90.68	6.846%	$96.888	$96.89	$96.90	$96.90
7 purchase totals =	$883.79		$958.8266	$958.83	$958.80	$958.90