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	$35.84	13.654%	$40.7336	$40.73	$40.75	$40.70
Purchase #2	$171.56	12.102%	$192.3222	$192.32	$192.30	$192.30
Purchase #3	$152.39	3.449%	$157.6459	$157.65	$157.65	$157.60
Purchase #4	$120.46	8.757%	$131.0087	$131.01	$131.00	$131.00
Purchase #5	$189.79	13.818%	$216.0152	$216.02	$216.00	$216.00
Purchase #6	$42.94	6.546%	$45.7509	$45.75	$45.75	$45.80
Purchase #7	$157.35	7.350%	$168.9152	$168.92	$168.90	$168.90
7 purchase totals =	$870.33		$952.3917	$952.40	$952.35	$952.30