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	$75.79	3.846%	$78.7049	$78.70	$78.70	$78.70
Purchase #2	$55.76	11.627%	$62.2432	$62.24	$62.25	$62.20
Purchase #3	$76.49	7.625%	$82.3224	$82.32	$82.30	$82.30
Purchase #4	$175.76	3.372%	$181.6866	$181.69	$181.70	$181.70
Purchase #5	$89.45	11.505%	$99.7412	$99.74	$99.75	$99.70
Purchase #6	$147.33	9.165%	$160.8328	$160.83	$160.85	$160.80
Purchase #7	$249.81	6.446%	$265.9128	$265.91	$265.90	$265.90
7 purchase totals =	$870.39		$931.4439	$931.43	$931.45	$931.30