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 $62.92   12.476%   $70.7699   $70.77   $70.75   $70.80  
  Purchase #2 $239.29   9.564%   $262.1757   $262.18   $262.20   $262.20  
  Purchase #3 $120.54   13.489%   $136.7996   $136.80   $136.80   $136.80  
  Purchase #4 $113.98   4.656%   $119.2869   $119.29   $119.30   $119.30  
  Purchase #5 $106.94   10.522%   $118.1922   $118.19   $118.20   $118.20  
  Purchase #6 $197.49   8.381%   $214.0416   $214.04   $214.05   $214.00  
  Purchase #7 $68.98   7.697%   $74.2894   $74.29   $74.30   $74.30  
  7 purchase totals = $910.14       $995.5553   $995.56   $995.60   $995.60