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	$67.74	5.245%	$71.293	$71.29	$71.30	$71.30
Purchase #2	$221.96	3.556%	$229.8529	$229.85	$229.85	$229.90
Purchase #3	$243.68	3.473%	$252.143	$252.14	$252.15	$252.10
Purchase #4	$155.57	12.400%	$174.8607	$174.86	$174.85	$174.90
Purchase #5	$165.58	12.250%	$185.8636	$185.86	$185.85	$185.90
Purchase #6	$96.78	3.368%	$100.0396	$100.04	$100.05	$100.00
Purchase #7	$195.67	7.224%	$209.8052	$209.81	$209.80	$209.80
7 purchase totals =	$1,146.98		$1,223.8580	$1,223.85	$1,223.85	$1,223.90