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 $92.43   8.468%   $100.257   $100.26   $100.25   $100.30  
  Purchase #2 $31.25   13.717%   $35.5366   $35.54   $35.55   $35.50  
  Purchase #3 $7.28   8.516%   $7.9   $7.90   $7.90   $7.90  
  Purchase #4 $201.36   12.711%   $226.9549   $226.95   $226.95   $227.00  
  Purchase #5 $197.89   5.719%   $209.2073   $209.21   $209.20   $209.20  
  Purchase #6 $188.90   13.691%   $214.7623   $214.76   $214.75   $214.80  
  Purchase #7 $147.34   5.737%   $155.7929   $155.79   $155.80   $155.80  
  7 purchase totals = $866.45       $950.4110   $950.41   $950.40   $950.50