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 $60.32   12.723%   $67.9945   $67.99   $68.00   $68.00  
  Purchase #2 $235.51   5.615%   $248.7339   $248.73   $248.75   $248.70  
  Purchase #3 $10.32   8.376%   $11.1844   $11.18   $11.20   $11.20  
  Purchase #4 $183.95   9.793%   $201.9642   $201.96   $201.95   $202.00  
  Purchase #5 $28.70   6.626%   $30.6017   $30.60   $30.60   $30.60  
  Purchase #6 $224.96   3.288%   $232.3567   $232.36   $232.35   $232.40  
  Purchase #7 $21.81   4.744%   $22.8447   $22.84   $22.85   $22.80  
  7 purchase totals = $765.57       $815.6801   $815.66   $815.70   $815.70