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 $186.92   10.503%   $206.5522   $206.55   $206.55   $206.60  
  Purchase #2 $150.28   4.402%   $156.8953   $156.90   $156.90   $156.90  
  Purchase #3 $107.81   11.812%   $120.5445   $120.54   $120.55   $120.50  
  Purchase #4 $241.53   4.599%   $252.638   $252.64   $252.65   $252.60  
  Purchase #5 $58.70   8.364%   $63.6097   $63.61   $63.60   $63.60  
  Purchase #6 $161.83   9.131%   $176.6067   $176.61   $176.60   $176.60  
  Purchase #7 $228.31   6.159%   $242.3716   $242.37   $242.35   $242.40  
  7 purchase totals = $1,135.38       $1,219.2180   $1,219.22   $1,219.20   $1,219.20