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	$31.85	5.164%	$33.4947	$33.49	$33.50	$33.50
Purchase #2	$68.88	13.702%	$78.3179	$78.32	$78.30	$78.30
Purchase #3	$166.57	11.560%	$185.8255	$185.83	$185.85	$185.80
Purchase #4	$96.42	10.140%	$106.197	$106.20	$106.20	$106.20
Purchase #5	$167.94	9.496%	$183.8876	$183.89	$183.90	$183.90
Purchase #6	$129.59	5.793%	$137.0971	$137.10	$137.10	$137.10
Purchase #7	$61.36	10.312%	$67.6874	$67.69	$67.70	$67.70
7 purchase totals =	$722.61		$792.5072	$792.52	$792.55	$792.50