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 $246.92   8.304%   $267.4242   $267.42   $267.40   $267.40  
  Purchase #2 $213.40   8.104%   $230.6939   $230.69   $230.70   $230.70  
  Purchase #3 $16.28   13.546%   $18.4853   $18.49   $18.50   $18.50  
  Purchase #4 $73.42   3.540%   $76.0191   $76.02   $76.00   $76.00  
  Purchase #5 $141.88   13.629%   $161.2168   $161.22   $161.20   $161.20  
  Purchase #6 $72.35   4.445%   $75.566   $75.57   $75.55   $75.60  
  Purchase #7 $22.46   9.670%   $24.6319   $24.63   $24.65   $24.60  
  7 purchase totals = $786.71       $854.0372   $854.04   $854.00   $854.00