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 $140.25   4.311%   $146.2962   $146.30   $146.30   $146.30  
  Purchase #2 $200.58   13.320%   $227.2973   $227.30   $227.30   $227.30  
  Purchase #3 $186.87   9.524%   $204.6675   $204.67   $204.65   $204.70  
  Purchase #4 $119.73   5.484%   $126.296   $126.30   $126.30   $126.30  
  Purchase #5 $149.74   4.422%   $156.3615   $156.36   $156.35   $156.40  
  Purchase #6 $41.84   4.805%   $43.8504   $43.85   $43.85   $43.90  
  Purchase #7 $228.62   3.438%   $236.48   $236.48   $236.50   $236.50  
  7 purchase totals = $1,067.63       $1,141.2489   $1,141.26   $1,141.25   $1,141.40