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 $247.62   4.740%   $259.3572   $259.36   $259.35   $259.40  
  Purchase #2 $41.90   13.678%   $47.6311   $47.63   $47.65   $47.60  
  Purchase #3 $26.83   3.574%   $27.7889   $27.79   $27.80   $27.80  
  Purchase #4 $211.36   5.217%   $222.3867   $222.39   $222.40   $222.40  
  Purchase #5 $146.92   6.258%   $156.1143   $156.11   $156.10   $156.10  
  Purchase #6 $153.38   4.803%   $160.7468   $160.75   $160.75   $160.70  
  Purchase #7 $177.62   4.521%   $185.6502   $185.65   $185.65   $185.70  
  7 purchase totals = $1,005.63       $1,059.6752   $1,059.68   $1,059.70   $1,059.70