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	$165.96	3.138%	$171.1678	$171.17	$171.15	$171.20
Purchase #2	$210.56	8.340%	$228.1207	$228.12	$228.10	$228.10
Purchase #3	$207.55	7.488%	$223.0913	$223.09	$223.10	$223.10
Purchase #4	$97.50	12.137%	$109.3336	$109.33	$109.35	$109.30
Purchase #5	$80.32	10.586%	$88.8227	$88.82	$88.80	$88.80
Purchase #6	$151.25	9.683%	$165.8955	$165.90	$165.90	$165.90
Purchase #7	$98.66	3.262%	$101.8783	$101.88	$101.90	$101.90
7 purchase totals =	$1,011.80		$1,088.3099	$1,088.31	$1,088.30	$1,088.30