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	$135.30	9.248%	$147.8125	$147.81	$147.80	$147.80
Purchase #2	$38.48	9.173%	$42.0098	$42.01	$42.00	$42.00
Purchase #3	$189.27	11.564%	$211.1572	$211.16	$211.15	$211.20
Purchase #4	$218.85	11.227%	$243.4203	$243.42	$243.40	$243.40
Purchase #5	$174.61	4.344%	$182.1951	$182.20	$182.20	$182.20
Purchase #6	$186.90	7.338%	$200.6147	$200.61	$200.60	$200.60
Purchase #7	$40.78	12.459%	$45.8608	$45.86	$45.85	$45.90
7 purchase totals =	$984.19		$1,073.0704	$1,073.07	$1,073.00	$1,073.10