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 $126.38   11.834%   $141.3358   $141.34   $141.35   $141.30  
  Purchase #2 $199.54   8.659%   $216.8182   $216.82   $216.80   $216.80  
  Purchase #3 $250.64   12.798%   $282.7169   $282.72   $282.70   $282.70  
  Purchase #4 $157.65   12.620%   $177.5454   $177.55   $177.55   $177.50  
  Purchase #5 $26.61   10.767%   $29.4751   $29.48   $29.50   $29.50  
  Purchase #6 $141.79   10.658%   $156.902   $156.90   $156.90   $156.90  
  Purchase #7 $124.63   8.187%   $134.8335   $134.83   $134.85   $134.80  
  7 purchase totals = $1,027.24       $1,139.6269   $1,139.64   $1,139.65   $1,139.50