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 $207.28   11.598%   $231.3203   $231.32   $231.30   $231.30  
  Purchase #2 $119.52   12.691%   $134.6883   $134.69   $134.70   $134.70  
  Purchase #3 $231.44   12.737%   $260.9185   $260.92   $260.90   $260.90  
  Purchase #4 $204.42   12.790%   $230.5653   $230.57   $230.55   $230.60  
  Purchase #5 $78.52   6.460%   $83.5924   $83.59   $83.60   $83.60  
  Purchase #6 $95.95   9.867%   $105.4174   $105.42   $105.40   $105.40  
  Purchase #7 $225.86   11.328%   $251.4454   $251.45   $251.45   $251.40  
  7 purchase totals = $1,162.99       $1,297.9476   $1,297.96   $1,297.90   $1,297.90