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	$100.85	4.275%	$105.1613	$105.16	$105.15	$105.20
Purchase #2	$69.31	10.110%	$76.3172	$76.32	$76.30	$76.30
Purchase #3	$206.73	12.773%	$233.1356	$233.14	$233.15	$233.10
Purchase #4	$169.89	12.745%	$191.5425	$191.54	$191.55	$191.50
Purchase #5	$67.42	5.863%	$71.3728	$71.37	$71.35	$71.40
Purchase #6	$74.43	11.492%	$82.9835	$82.98	$83.00	$83.00
Purchase #7	$234.59	3.676%	$243.2135	$243.21	$243.20	$243.20
7 purchase totals =	$923.22		$1,003.7264	$1,003.72	$1,003.70	$1,003.70