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 $156.28   4.569%   $163.4204   $163.42   $163.40   $163.40  
  Purchase #2 $232.76   7.719%   $250.7267   $250.73   $250.75   $250.70  
  Purchase #3 $23.80   8.277%   $25.7699   $25.77   $25.75   $25.80  
  Purchase #4 $147.64   3.163%   $152.3099   $152.31   $152.30   $152.30  
  Purchase #5 $127.31   12.571%   $143.3141   $143.31   $143.30   $143.30  
  Purchase #6 $48.54   12.371%   $54.5449   $54.54   $54.55   $54.50  
  Purchase #7 $187.70   9.242%   $205.0472   $205.05   $205.05   $205.00  
  7 purchase totals = $924.03       $995.1331   $995.13   $995.10   $995.00