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	$83.41	9.370%	$91.2255	$91.23	$91.25	$91.20
Purchase #2	$127.80	9.410%	$139.826	$139.83	$139.85	$139.80
Purchase #3	$79.39	11.623%	$88.6175	$88.62	$88.60	$88.60
Purchase #4	$105.96	4.552%	$110.7833	$110.78	$110.80	$110.80
Purchase #5	$164.56	4.473%	$171.9208	$171.92	$171.90	$171.90
Purchase #6	$63.90	11.424%	$71.1999	$71.20	$71.20	$71.20
Purchase #7	$35.39	3.750%	$36.7171	$36.72	$36.70	$36.70
7 purchase totals =	$660.41		$710.2901	$710.30	$710.30	$710.20