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 $50.32   10.649%   $55.6786   $55.68   $55.70   $55.70  
  Purchase #2 $223.95   5.796%   $236.9301   $236.93   $236.95   $236.90  
  Purchase #3 $145.45   8.768%   $158.2031   $158.20   $158.20   $158.20  
  Purchase #4 $238.85   3.661%   $247.5943   $247.59   $247.60   $247.60  
  Purchase #5 $8.68   7.353%   $9.3182   $9.32   $9.30   $9.30  
  Purchase #6 $111.35   13.718%   $126.625   $126.63   $126.65   $126.60  
  Purchase #7 $172.44   6.438%   $183.5417   $183.54   $183.55   $183.50  
  7 purchase totals = $951.04       $1,017.8910   $1,017.89   $1,017.95   $1,017.80