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 $246.32   11.624%   $274.9522   $274.95   $274.95   $275.00  
  Purchase #2 $70.34   4.742%   $73.6755   $73.68   $73.70   $73.70  
  Purchase #3 $183.27   7.852%   $197.6604   $197.66   $197.65   $197.70  
  Purchase #4 $135.26   3.685%   $140.2443   $140.24   $140.25   $140.20  
  Purchase #5 $125.68   10.270%   $138.5873   $138.59   $138.60   $138.60  
  Purchase #6 $95.64   10.470%   $105.6535   $105.65   $105.65   $105.70  
  Purchase #7 $97.95   5.143%   $102.9876   $102.99   $103.00   $103.00  
  7 purchase totals = $954.46       $1,033.7608   $1,033.76   $1,033.80   $1,033.90