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 $53.89   12.816%   $60.7965   $60.80   $60.80   $60.80  
  Purchase #2 $221.54   13.364%   $251.1466   $251.15   $251.15   $251.10  
  Purchase #3 $149.59   10.846%   $165.8145   $165.81   $165.80   $165.80  
  Purchase #4 $196.27   13.499%   $222.7645   $222.76   $222.75   $222.80  
  Purchase #5 $86.27   12.552%   $97.0986   $97.10   $97.10   $97.10  
  Purchase #6 $224.69   12.360%   $252.4617   $252.46   $252.45   $252.50  
  Purchase #7 $166.51   12.736%   $187.7167   $187.72   $187.70   $187.70  
  7 purchase totals = $1,098.76       $1,237.7991   $1,237.80   $1,237.75   $1,237.80