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 $52.75   6.545%   $56.2025   $56.20   $56.20   $56.20  
  Purchase #2 $166.53   8.831%   $181.2363   $181.24   $181.25   $181.20  
  Purchase #3 $230.75   4.727%   $241.6576   $241.66   $241.65   $241.70  
  Purchase #4 $215.75   4.544%   $225.5537   $225.55   $225.55   $225.60  
  Purchase #5 $17.44   8.631%   $18.9452   $18.95   $18.95   $18.90  
  Purchase #6 $245.74   6.536%   $261.8016   $261.80   $261.80   $261.80  
  Purchase #7 $36.84   3.410%   $38.0962   $38.10   $38.10   $38.10  
  7 purchase totals = $965.80       $1,023.4931   $1,023.50   $1,023.50   $1,023.50