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 $236.59   10.295%   $260.9469   $260.95   $260.95   $260.90  
  Purchase #2 $105.28   5.163%   $110.7156   $110.72   $110.70   $110.70  
  Purchase #3 $75.87   5.197%   $79.813   $79.81   $79.80   $79.80  
  Purchase #4 $181.35   3.286%   $187.3092   $187.31   $187.30   $187.30  
  Purchase #5 $169.42   7.795%   $182.6263   $182.63   $182.65   $182.60  
  Purchase #6 $207.48   7.864%   $223.7962   $223.80   $223.80   $223.80  
  Purchase #7 $142.83   4.119%   $148.7132   $148.71   $148.70   $148.70  
  7 purchase totals = $1,118.82       $1,193.9204   $1,193.93   $1,193.90   $1,193.80