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 $180.28   13.712%   $205   $205.00   $205.00   $205.00  
  Purchase #2 $75.55   5.151%   $79.4416   $79.44   $79.45   $79.40  
  Purchase #3 $238.69   11.771%   $266.7862   $266.79   $266.80   $266.80  
  Purchase #4 $116.48   6.872%   $124.4845   $124.48   $124.50   $124.50  
  Purchase #5 $83.39   5.735%   $88.1724   $88.17   $88.15   $88.20  
  Purchase #6 $26.57   7.873%   $28.6619   $28.66   $28.65   $28.70  
  Purchase #7 $199.73   7.865%   $215.4388   $215.44   $215.45   $215.40  
  7 purchase totals = $920.69       $1,007.9854   $1,007.98   $1,008.00   $1,008.00