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 $146.86   13.443%   $166.6024   $166.60   $166.60   $166.60  
  Purchase #2 $59.60   4.333%   $62.1825   $62.18   $62.20   $62.20  
  Purchase #3 $235.97   3.873%   $245.1091   $245.11   $245.10   $245.10  
  Purchase #4 $37.72   6.197%   $40.0575   $40.06   $40.05   $40.10  
  Purchase #5 $136.68   6.617%   $145.7241   $145.72   $145.70   $145.70  
  Purchase #6 $80.77   6.517%   $86.0338   $86.03   $86.05   $86.00  
  Purchase #7 $245.65   13.338%   $278.4148   $278.41   $278.40   $278.40  
  7 purchase totals = $943.25       $1,024.1242   $1,024.11   $1,024.10   $1,024.10