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	$138.88	6.203%	$147.4947	$147.49	$147.50	$147.50
Purchase #2	$181.55	3.580%	$188.0495	$188.05	$188.05	$188.00
Purchase #3	$36.69	9.501%	$40.1759	$40.18	$40.20	$40.20
Purchase #4	$27.41	5.579%	$28.9392	$28.94	$28.95	$28.90
Purchase #5	$79.86	3.425%	$82.5952	$82.60	$82.60	$82.60
Purchase #6	$23.61	7.191%	$25.3078	$25.31	$25.30	$25.30
Purchase #7	$57.35	3.819%	$59.5402	$59.54	$59.55	$59.50
7 purchase totals =	$545.35		$572.1025	$572.11	$572.15	$572.00