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 $245.78   3.796%   $255.1098   $255.11   $255.10   $255.10  
  Purchase #2 $180.87   6.395%   $192.4366   $192.44   $192.45   $192.40  
  Purchase #3 $202.35   12.665%   $227.9776   $227.98   $228.00   $228.00  
  Purchase #4 $53.86   12.772%   $60.739   $60.74   $60.75   $60.70  
  Purchase #5 $110.31   13.586%   $125.2967   $125.30   $125.30   $125.30  
  Purchase #6 $182.41   8.719%   $198.3143   $198.31   $198.30   $198.30  
  Purchase #7 $5.25   7.866%   $5.663   $5.66   $5.65   $5.70  
  7 purchase totals = $980.83       $1,065.5370   $1,065.54   $1,065.55   $1,065.50