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	$31.65	6.112%	$33.5844	$33.58	$33.60	$33.60
Purchase #2	$55.61	11.319%	$61.9045	$61.90	$61.90	$61.90
Purchase #3	$199.31	12.321%	$223.867	$223.87	$223.85	$223.90
Purchase #4	$147.47	11.691%	$164.7107	$164.71	$164.70	$164.70
Purchase #5	$250.71	12.450%	$281.9234	$281.92	$281.90	$281.90
Purchase #6	$234.34	6.180%	$248.8222	$248.82	$248.80	$248.80
Purchase #7	$224.96	11.221%	$250.2028	$250.20	$250.20	$250.20
7 purchase totals =	$1,144.05		$1,265.0150	$1,265.00	$1,264.95	$1,265.00