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 $95.62   9.869%   $105.0567   $105.06   $105.05   $105.10  
  Purchase #2 $140.73   11.727%   $157.2334   $157.23   $157.25   $157.20  
  Purchase #3 $114.93   9.600%   $125.9633   $125.96   $125.95   $126.00  
  Purchase #4 $14.27   8.379%   $15.4657   $15.47   $15.45   $15.50  
  Purchase #5 $238.41   8.630%   $258.9848   $258.98   $259.00   $259.00  
  Purchase #6 $181.35   4.415%   $189.3566   $189.36   $189.35   $189.40  
  Purchase #7 $111.36   11.318%   $123.9637   $123.96   $123.95   $124.00  
  7 purchase totals = $896.67       $976.0242   $976.02   $976.00   $976.20