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 $91.63   13.156%   $103.6848   $103.68   $103.70   $103.70  
  Purchase #2 $71.55   4.740%   $74.9415   $74.94   $74.95   $74.90  
  Purchase #3 $64.77   6.704%   $69.1122   $69.11   $69.10   $69.10  
  Purchase #4 $88.67   7.868%   $95.6466   $95.65   $95.65   $95.60  
  Purchase #5 $203.41   8.394%   $220.4842   $220.48   $220.50   $220.50  
  Purchase #6 $239.89   6.260%   $254.9071   $254.91   $254.90   $254.90  
  Purchase #7 $133.74   11.235%   $148.7657   $148.77   $148.75   $148.80  
  7 purchase totals = $893.66       $967.5421   $967.54   $967.55   $967.50