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	$242.46	13.796%	$275.9098	$275.91	$275.90	$275.90
Purchase #2	$110.89	7.812%	$119.5527	$119.55	$119.55	$119.60
Purchase #3	$71.32	6.316%	$75.8246	$75.82	$75.80	$75.80
Purchase #4	$191.27	7.357%	$205.3417	$205.34	$205.35	$205.30
Purchase #5	$219.52	11.142%	$243.9789	$243.98	$244.00	$244.00
Purchase #6	$197.39	13.358%	$223.7574	$223.76	$223.75	$223.80
Purchase #7	$27.39	13.633%	$31.1241	$31.12	$31.10	$31.10
7 purchase totals =	$1,060.24		$1,175.4892	$1,175.48	$1,175.45	$1,175.50