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 $41.95   10.541%   $46.3719   $46.37   $46.35   $46.40  
  Purchase #2 $190.74   7.316%   $204.6945   $204.69   $204.70   $204.70  
  Purchase #3 $239.89   6.168%   $254.6864   $254.69   $254.70   $254.70  
  Purchase #4 $66.87   9.148%   $72.9873   $72.99   $73.00   $73.00  
  Purchase #5 $204.74   8.578%   $222.3026   $222.30   $222.30   $222.30  
  Purchase #6 $81.30   7.491%   $87.3902   $87.39   $87.40   $87.40  
  Purchase #7 $90.77   13.102%   $102.6627   $102.66   $102.65   $102.70  
  7 purchase totals = $916.26       $991.0956   $991.09   $991.10   $991.20