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 $99.28   6.826%   $106.0569   $106.06   $106.05   $106.10  
  Purchase #2 $123.30   10.544%   $136.3008   $136.30   $136.30   $136.30  
  Purchase #3 $80.63   5.754%   $85.2695   $85.27   $85.25   $85.30  
  Purchase #4 $171.39   12.417%   $192.6715   $192.67   $192.65   $192.70  
  Purchase #5 $241.56   9.243%   $263.8874   $263.89   $263.90   $263.90  
  Purchase #6 $152.69   12.522%   $171.8098   $171.81   $171.80   $171.80  
  Purchase #7 $52.98   9.720%   $58.1297   $58.13   $58.15   $58.10  
  7 purchase totals = $921.83       $1,014.1256   $1,014.13   $1,014.10   $1,014.20