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	$221.98	4.212%	$231.3298	$231.33	$231.35	$231.30
Purchase #2	$112.78	6.669%	$120.3013	$120.30	$120.30	$120.30
Purchase #3	$82.36	11.355%	$91.712	$91.71	$91.70	$91.70
Purchase #4	$246.84	11.546%	$275.3401	$275.34	$275.35	$275.30
Purchase #5	$181.56	8.471%	$196.9399	$196.94	$196.95	$196.90
Purchase #6	$78.41	12.361%	$88.1023	$88.10	$88.10	$88.10
Purchase #7	$164.93	13.105%	$186.5441	$186.54	$186.55	$186.50
7 purchase totals =	$1,088.86		$1,190.2695	$1,190.26	$1,190.30	$1,190.10