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 $9.68   3.318%   $10.0012   $10.00   $10.00   $10.00  
  Purchase #2 $103.63   13.272%   $117.3838   $117.38   $117.40   $117.40  
  Purchase #3 $216.82   12.435%   $243.7816   $243.78   $243.80   $243.80  
  Purchase #4 $128.39   9.484%   $140.5665   $140.57   $140.55   $140.60  
  Purchase #5 $174.51   13.724%   $198.4598   $198.46   $198.45   $198.50  
  Purchase #6 $114.41   12.252%   $128.4275   $128.43   $128.45   $128.40  
  Purchase #7 $39.75   12.182%   $44.5923   $44.59   $44.60   $44.60  
  7 purchase totals = $787.19       $883.2127   $883.21   $883.25   $883.30