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 $218.62   7.257%   $234.4853   $234.49   $234.50   $234.50  
  Purchase #2 $249.30   6.548%   $265.6242   $265.62   $265.60   $265.60  
  Purchase #3 $201.42   13.310%   $228.229   $228.23   $228.25   $228.20  
  Purchase #4 $82.86   11.698%   $92.553   $92.55   $92.55   $92.60  
  Purchase #5 $211.79   3.255%   $218.6838   $218.68   $218.70   $218.70  
  Purchase #6 $61.31   7.873%   $66.1369   $66.14   $66.15   $66.10  
  Purchase #7 $39.26   11.820%   $43.9005   $43.90   $43.90   $43.90  
  7 purchase totals = $1,064.56       $1,149.6127   $1,149.61   $1,149.65   $1,149.60