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	$58.84	5.578%	$62.1221	$62.12	$62.10	$62.10
Purchase #2	$192.30	8.874%	$209.3647	$209.36	$209.35	$209.40
Purchase #3	$83.91	6.434%	$89.3088	$89.31	$89.30	$89.30
Purchase #4	$31.44	13.767%	$35.7683	$35.77	$35.75	$35.80
Purchase #5	$140.67	11.330%	$156.6079	$156.61	$156.60	$156.60
Purchase #6	$128.37	3.800%	$133.2481	$133.25	$133.25	$133.20
Purchase #7	$160.37	6.832%	$171.3265	$171.33	$171.35	$171.30
7 purchase totals =	$795.90		$857.7464	$857.75	$857.70	$857.70