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 $226.44   13.668%   $257.3898   $257.39   $257.40   $257.40  
  Purchase #2 $75.42   4.634%   $78.915   $78.92   $78.90   $78.90  
  Purchase #3 $41.30   7.152%   $44.2538   $44.25   $44.25   $44.30  
  Purchase #4 $156.40   11.201%   $173.9184   $173.92   $173.90   $173.90  
  Purchase #5 $198.70   6.691%   $211.995   $212.00   $212.00   $212.00  
  Purchase #6 $69.55   6.122%   $73.8079   $73.81   $73.80   $73.80  
  Purchase #7 $22.85   13.856%   $26.0161   $26.02   $26.00   $26.00  
  7 purchase totals = $790.66       $866.2960   $866.31   $866.25   $866.30