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 $247.81   5.227%   $260.763   $260.76   $260.75   $260.80  
  Purchase #2 $89.42   6.721%   $95.4299   $95.43   $95.45   $95.40  
  Purchase #3 $181.45   5.661%   $191.7219   $191.72   $191.70   $191.70  
  Purchase #4 $53.41   8.201%   $57.7902   $57.79   $57.80   $57.80  
  Purchase #5 $105.35   8.806%   $114.6271   $114.63   $114.65   $114.60  
  Purchase #6 $73.88   8.614%   $80.244   $80.24   $80.25   $80.20  
  Purchase #7 $8.97   6.364%   $9.5409   $9.54   $9.55   $9.50  
  7 purchase totals = $760.29       $810.1170   $810.11   $810.15   $810.00