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	$232.46	4.187%	$242.1931	$242.19	$242.20	$242.20
Purchase #2	$152.31	8.112%	$164.6654	$164.67	$164.65	$164.70
Purchase #3	$35.82	11.506%	$39.9414	$39.94	$39.95	$39.90
Purchase #4	$240.50	8.644%	$261.2888	$261.29	$261.30	$261.30
Purchase #5	$90.46	6.830%	$96.6384	$96.64	$96.65	$96.60
Purchase #6	$151.76	13.182%	$171.765	$171.77	$171.75	$171.80
Purchase #7	$61.89	8.845%	$67.3642	$67.36	$67.35	$67.40
7 purchase totals =	$965.20		$1,043.8563	$1,043.86	$1,043.85	$1,043.90