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 $57.85   4.253%   $60.3104   $60.31   $60.30   $60.30  
  Purchase #2 $225.95   7.837%   $243.6577   $243.66   $243.65   $243.70  
  Purchase #3 $95.61   11.857%   $106.9465   $106.95   $106.95   $106.90  
  Purchase #4 $250.25   3.511%   $259.0363   $259.04   $259.05   $259.00  
  Purchase #5 $24.56   11.866%   $27.4743   $27.47   $27.45   $27.50  
  Purchase #6 $238.79   9.326%   $261.0596   $261.06   $261.05   $261.10  
  Purchase #7 $51.72   5.457%   $54.5424   $54.54   $54.55   $54.50  
  7 purchase totals = $944.73       $1,013.0272   $1,013.03   $1,013.00   $1,013.00