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 $46.36   7.312%   $49.7498   $49.75   $49.75   $49.70  
  Purchase #2 $153.33   6.109%   $162.6969   $162.70   $162.70   $162.70  
  Purchase #3 $248.70   11.446%   $277.1662   $277.17   $277.15   $277.20  
  Purchase #4 $209.68   6.863%   $224.0703   $224.07   $224.05   $224.10  
  Purchase #5 $50.79   10.683%   $56.2159   $56.22   $56.20   $56.20  
  Purchase #6 $234.49   6.846%   $250.5432   $250.54   $250.55   $250.50  
  Purchase #7 $107.93   12.359%   $121.2691   $121.27   $121.25   $121.30  
  7 purchase totals = $1,051.28       $1,141.7114   $1,141.72   $1,141.65   $1,141.70