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	$180.81	12.398%	$203.2268	$203.23	$203.25	$203.20
Purchase #2	$35.79	12.629%	$40.3099	$40.31	$40.30	$40.30
Purchase #3	$198.69	6.626%	$211.8552	$211.86	$211.85	$211.90
Purchase #4	$104.52	13.820%	$118.9647	$118.96	$118.95	$119.00
Purchase #5	$38.52	6.148%	$40.8882	$40.89	$40.90	$40.90
Purchase #6	$25.63	10.766%	$28.3893	$28.39	$28.40	$28.40
Purchase #7	$50.55	11.543%	$56.385	$56.39	$56.40	$56.40
7 purchase totals =	$634.51		$700.0191	$700.03	$700.05	$700.10