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 $193.36   5.629%   $204.2442   $204.24   $204.25   $204.20  
  Purchase #2 $41.67   11.210%   $46.3412   $46.34   $46.35   $46.30  
  Purchase #3 $169.91   4.102%   $176.8797   $176.88   $176.90   $176.90  
  Purchase #4 $125.74   13.414%   $142.6068   $142.61   $142.60   $142.60  
  Purchase #5 $217.41   7.775%   $234.3136   $234.31   $234.30   $234.30  
  Purchase #6 $28.54   11.374%   $31.7861   $31.79   $31.80   $31.80  
  Purchase #7 $204.37   8.859%   $222.4751   $222.48   $222.50   $222.50  
  7 purchase totals = $981.00       $1,058.6467   $1,058.65   $1,058.70   $1,058.60