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 $203.34   10.448%   $224.585   $224.59   $224.60   $224.60  
  Purchase #2 $27.32   13.282%   $30.9486   $30.95   $30.95   $30.90  
  Purchase #3 $27.55   10.339%   $30.3984   $30.40   $30.40   $30.40  
  Purchase #4 $69.43   12.835%   $78.3413   $78.34   $78.35   $78.30  
  Purchase #5 $44.55   7.322%   $47.812   $47.81   $47.80   $47.80  
  Purchase #6 $219.47   13.371%   $248.8153   $248.82   $248.80   $248.80  
  Purchase #7 $232.31   13.648%   $264.0157   $264.02   $264.00   $264.00  
  7 purchase totals = $823.97       $924.9163   $924.93   $924.90   $924.80