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	$83.94	6.167%	$89.1166	$89.12	$89.10	$89.10
Purchase #2	$87.57	6.765%	$93.4941	$93.49	$93.50	$93.50
Purchase #3	$203.62	10.531%	$225.0632	$225.06	$225.05	$225.10
Purchase #4	$100.61	4.470%	$105.1073	$105.11	$105.10	$105.10
Purchase #5	$211.67	6.871%	$226.2138	$226.21	$226.20	$226.20
Purchase #6	$101.33	3.777%	$105.1572	$105.16	$105.15	$105.20
Purchase #7	$152.57	7.518%	$164.0402	$164.04	$164.05	$164.00
7 purchase totals =	$941.31		$1,008.1924	$1,008.19	$1,008.15	$1,008.20