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 $62.88   7.234%   $67.4287   $67.43   $67.45   $67.40  
  Purchase #2 $250.68   8.517%   $272.0304   $272.03   $272.05   $272.00  
  Purchase #3 $171.33   9.454%   $187.5275   $187.53   $187.55   $187.50  
  Purchase #4 $234.49   5.104%   $246.4584   $246.46   $246.45   $246.50  
  Purchase #5 $15.82   9.327%   $17.2955   $17.30   $17.30   $17.30  
  Purchase #6 $22.72   13.503%   $25.7879   $25.79   $25.80   $25.80  
  Purchase #7 $166.36   13.565%   $188.9267   $188.93   $188.95   $188.90  
  7 purchase totals = $924.28       $1,005.4551   $1,005.47   $1,005.55   $1,005.40