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 $224.33   8.535%   $243.4766   $243.48   $243.50   $243.50  
  Purchase #2 $78.67   3.509%   $81.4305   $81.43   $81.45   $81.40  
  Purchase #3 $206.99   3.397%   $214.0215   $214.02   $214.00   $214.00  
  Purchase #4 $59.55   11.616%   $66.4673   $66.47   $66.45   $66.50  
  Purchase #5 $66.47   7.299%   $71.3216   $71.32   $71.30   $71.30  
  Purchase #6 $69.25   8.377%   $75.0511   $75.05   $75.05   $75.10  
  Purchase #7 $89.94   7.314%   $96.5182   $96.52   $96.50   $96.50  
  7 purchase totals = $795.20       $848.2868   $848.29   $848.25   $848.30