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	$123.50	11.413%	$137.5951	$137.60	$137.60	$137.60
Purchase #2	$57.33	12.756%	$64.643	$64.64	$64.65	$64.60
Purchase #3	$27.64	3.115%	$28.501	$28.50	$28.50	$28.50
Purchase #4	$237.84	10.651%	$263.1723	$263.17	$263.15	$263.20
Purchase #5	$31.60	8.292%	$34.2203	$34.22	$34.20	$34.20
Purchase #6	$88.40	12.695%	$99.6224	$99.62	$99.60	$99.60
Purchase #7	$194.48	7.778%	$209.6067	$209.61	$209.60	$209.60
7 purchase totals =	$760.79		$837.3608	$837.36	$837.30	$837.30