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 $153.49   5.818%   $162.42   $162.42   $162.40   $162.40  
  Purchase #2 $179.70   12.208%   $201.6378   $201.64   $201.65   $201.60  
  Purchase #3 $21.59   11.432%   $24.0582   $24.06   $24.05   $24.10  
  Purchase #4 $115.69   7.366%   $124.2117   $124.21   $124.20   $124.20  
  Purchase #5 $216.79   13.126%   $245.2459   $245.25   $245.25   $245.20  
  Purchase #6 $195.59   6.111%   $207.5425   $207.54   $207.55   $207.50  
  Purchase #7 $96.95   13.577%   $110.1129   $110.11   $110.10   $110.10  
  7 purchase totals = $979.80       $1,075.2290   $1,075.23   $1,075.20   $1,075.10