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	$76.92	8.118%	$83.1644	$83.16	$83.15	$83.20
Purchase #2	$39.74	13.678%	$45.1756	$45.18	$45.20	$45.20
Purchase #3	$198.31	9.873%	$217.8891	$217.89	$217.90	$217.90
Purchase #4	$71.46	13.289%	$80.9563	$80.96	$80.95	$81.00
Purchase #5	$222.49	12.431%	$250.1477	$250.15	$250.15	$250.10
Purchase #6	$228.54	6.293%	$242.922	$242.92	$242.90	$242.90
Purchase #7	$228.96	6.465%	$243.7623	$243.76	$243.75	$243.80
7 purchase totals =	$1,066.42		$1,164.0174	$1,164.02	$1,164.00	$1,164.10