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 $56.54   8.235%   $61.1961   $61.20   $61.20   $61.20  
  Purchase #2 $246.44   10.753%   $272.9397   $272.94   $272.95   $272.90  
  Purchase #3 $200.34   7.524%   $215.4136   $215.41   $215.40   $215.40  
  Purchase #4 $131.95   12.497%   $148.4398   $148.44   $148.45   $148.40  
  Purchase #5 $39.57   5.644%   $41.8033   $41.80   $41.80   $41.80  
  Purchase #6 $121.59   12.251%   $136.486   $136.49   $136.50   $136.50  
  Purchase #7 $186.81   9.448%   $204.4598   $204.46   $204.45   $204.50  
  7 purchase totals = $983.24       $1,080.7383   $1,080.74   $1,080.75   $1,080.70