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	$180.97	3.571%	$187.4324	$187.43	$187.45	$187.40
Purchase #2	$189.32	11.582%	$211.247	$211.25	$211.25	$211.20
Purchase #3	$185.71	12.192%	$208.3518	$208.35	$208.35	$208.40
Purchase #4	$6.97	7.545%	$7.4959	$7.50	$7.50	$7.50
Purchase #5	$247.45	11.497%	$275.8993	$275.90	$275.90	$275.90
Purchase #6	$85.85	6.658%	$91.5659	$91.57	$91.55	$91.60
Purchase #7	$237.68	3.142%	$245.1479	$245.15	$245.15	$245.10
7 purchase totals =	$1,133.95		$1,227.1402	$1,227.15	$1,227.15	$1,227.10