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	$90.72	8.337%	$98.2833	$98.28	$98.30	$98.30
Purchase #2	$185.37	6.477%	$197.3764	$197.38	$197.40	$197.40
Purchase #3	$241.61	9.451%	$264.4446	$264.44	$264.45	$264.40
Purchase #4	$121.64	7.731%	$131.044	$131.04	$131.05	$131.00
Purchase #5	$31.69	11.862%	$35.4491	$35.45	$35.45	$35.40
Purchase #6	$80.25	9.755%	$88.0784	$88.08	$88.10	$88.10
Purchase #7	$73.36	12.819%	$82.764	$82.76	$82.75	$82.80
7 purchase totals =	$824.64		$897.4398	$897.43	$897.50	$897.40