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 $59.29   11.403%   $66.0508   $66.05   $66.05   $66.10  
  Purchase #2 $199.93   8.570%   $217.064   $217.06   $217.05   $217.10  
  Purchase #3 $49.55   5.769%   $52.4085   $52.41   $52.40   $52.40  
  Purchase #4 $250.86   9.713%   $275.226   $275.23   $275.25   $275.20  
  Purchase #5 $192.39   6.156%   $204.2335   $204.23   $204.25   $204.20  
  Purchase #6 $204.80   11.337%   $228.0182   $228.02   $228.00   $228.00  
  Purchase #7 $236.26   10.686%   $261.5067   $261.51   $261.50   $261.50  
  7 purchase totals = $1,193.08       $1,304.5077   $1,304.51   $1,304.50   $1,304.50