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 $246.32   10.743%   $272.7822   $272.78   $272.80   $272.80  
  Purchase #2 $164.91   4.253%   $171.9236   $171.92   $171.90   $171.90  
  Purchase #3 $103.60   4.620%   $108.3863   $108.39   $108.40   $108.40  
  Purchase #4 $33.80   11.547%   $37.7029   $37.70   $37.70   $37.70  
  Purchase #5 $217.50   11.206%   $241.8731   $241.87   $241.85   $241.90  
  Purchase #6 $104.77   13.675%   $119.0973   $119.10   $119.10   $119.10  
  Purchase #7 $101.63   5.266%   $106.9818   $106.98   $107.00   $107.00  
  7 purchase totals = $972.53       $1,058.7472   $1,058.74   $1,058.75   $1,058.80