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	$247.76	5.327%	$260.9582	$260.96	$260.95	$261.00
Purchase #2	$57.84	4.221%	$60.2814	$60.28	$60.30	$60.30
Purchase #3	$72.73	7.266%	$78.0146	$78.01	$78.00	$78.00
Purchase #4	$154.73	6.224%	$164.3604	$164.36	$164.35	$164.40
Purchase #5	$147.46	11.621%	$164.5963	$164.60	$164.60	$164.60
Purchase #6	$174.72	11.136%	$194.1768	$194.18	$194.20	$194.20
Purchase #7	$58.93	4.362%	$61.5005	$61.50	$61.50	$61.50
7 purchase totals =	$914.17		$983.8882	$983.89	$983.90	$984.00