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	$158.52	6.511%	$168.8412	$168.84	$168.85	$168.80
Purchase #2	$250.57	12.188%	$281.1095	$281.11	$281.10	$281.10
Purchase #3	$118.44	7.143%	$126.9002	$126.90	$126.90	$126.90
Purchase #4	$193.88	3.217%	$200.1171	$200.12	$200.10	$200.10
Purchase #5	$84.91	10.767%	$94.0523	$94.05	$94.05	$94.10
Purchase #6	$37.96	13.555%	$43.1055	$43.11	$43.10	$43.10
Purchase #7	$43.78	4.802%	$45.8823	$45.88	$45.90	$45.90
7 purchase totals =	$888.06		$960.0081	$960.01	$960.00	$960.00