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 $206.66   9.485%   $226.2617   $226.26   $226.25   $226.30  
  Purchase #2 $227.88   10.862%   $252.6323   $252.63   $252.65   $252.60  
  Purchase #3 $5.38   4.248%   $5.6085   $5.61   $5.60   $5.60  
  Purchase #4 $160.43   3.678%   $166.3306   $166.33   $166.35   $166.30  
  Purchase #5 $207.36   8.705%   $225.4107   $225.41   $225.40   $225.40  
  Purchase #6 $72.80   10.623%   $80.5335   $80.53   $80.55   $80.50  
  Purchase #7 $151.73   12.627%   $170.8889   $170.89   $170.90   $170.90  
  7 purchase totals = $1,032.24       $1,127.6662   $1,127.66   $1,127.70   $1,127.60