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 $38.51   12.546%   $43.3415   $43.34   $43.35   $43.30  
  Purchase #2 $212.95   6.351%   $226.4745   $226.47   $226.45   $226.50  
  Purchase #3 $45.29   3.800%   $47.011   $47.01   $47.00   $47.00  
  Purchase #4 $127.46   9.562%   $139.6477   $139.65   $139.65   $139.60  
  Purchase #5 $40.87   7.809%   $44.0615   $44.06   $44.05   $44.10  
  Purchase #6 $126.65   8.634%   $137.585   $137.59   $137.60   $137.60  
  Purchase #7 $247.44   5.656%   $261.4352   $261.44   $261.45   $261.40  
  7 purchase totals = $839.17       $899.5564   $899.56   $899.55   $899.50