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 $22.93   8.724%   $24.9304   $24.93   $24.95   $24.90  
  Purchase #2 $246.25   3.415%   $254.6594   $254.66   $254.65   $254.70  
  Purchase #3 $118.28   10.595%   $130.8118   $130.81   $130.80   $130.80  
  Purchase #4 $210.60   11.435%   $234.6821   $234.68   $234.70   $234.70  
  Purchase #5 $82.71   9.725%   $90.7535   $90.75   $90.75   $90.80  
  Purchase #6 $146.80   13.278%   $166.2921   $166.29   $166.30   $166.30  
  Purchase #7 $176.35   9.604%   $193.2867   $193.29   $193.30   $193.30  
  7 purchase totals = $1,003.92       $1,095.4160   $1,095.41   $1,095.45   $1,095.50