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	$250.70	12.360%	$281.6865	$281.69	$281.70	$281.70
Purchase #2	$136.69	11.378%	$152.2426	$152.24	$152.25	$152.20
Purchase #3	$198.83	5.355%	$209.4773	$209.48	$209.50	$209.50
Purchase #4	$55.27	11.346%	$61.5409	$61.54	$61.55	$61.50
Purchase #5	$85.63	3.741%	$88.8334	$88.83	$88.85	$88.80
Purchase #6	$191.85	10.124%	$211.2729	$211.27	$211.25	$211.30
Purchase #7	$73.53	3.223%	$75.8999	$75.90	$75.90	$75.90
7 purchase totals =	$992.50		$1,080.9535	$1,080.95	$1,081.00	$1,080.90