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 $67.86   8.543%   $73.6573   $73.66   $73.65   $73.70  
  Purchase #2 $201.53   3.691%   $208.9685   $208.97   $208.95   $209.00  
  Purchase #3 $19.77   8.654%   $21.4809   $21.48   $21.50   $21.50  
  Purchase #4 $214.85   12.250%   $241.1691   $241.17   $241.15   $241.20  
  Purchase #5 $235.34   13.264%   $266.5555   $266.56   $266.55   $266.60  
  Purchase #6 $230.43   3.459%   $238.4006   $238.40   $238.40   $238.40  
  Purchase #7 $12.98   3.441%   $13.4266   $13.43   $13.45   $13.40  
  7 purchase totals = $982.76       $1,063.6585   $1,063.67   $1,063.65   $1,063.80