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 $249.51   7.868%   $269.1414   $269.14   $269.15   $269.10  
  Purchase #2 $19.88   13.326%   $22.5292   $22.53   $22.55   $22.50  
  Purchase #3 $224.66   10.550%   $248.3616   $248.36   $248.35   $248.40  
  Purchase #4 $24.81   5.551%   $26.1872   $26.19   $26.20   $26.20  
  Purchase #5 $220.71   6.455%   $234.9568   $234.96   $234.95   $235.00  
  Purchase #6 $200.42   4.867%   $210.1744   $210.17   $210.15   $210.20  
  Purchase #7 $136.32   9.442%   $149.1913   $149.19   $149.20   $149.20  
  7 purchase totals = $1,076.31       $1,160.5419   $1,160.54   $1,160.55   $1,160.60