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 $155.63   9.402%   $170.2623   $170.26   $170.25   $170.30  
  Purchase #2 $216.28   8.868%   $235.4597   $235.46   $235.45   $235.50  
  Purchase #3 $136.54   9.298%   $149.2355   $149.24   $149.25   $149.20  
  Purchase #4 $247.72   3.627%   $256.7048   $256.70   $256.70   $256.70  
  Purchase #5 $138.91   5.108%   $146.0055   $146.01   $146.00   $146.00  
  Purchase #6 $58.49   3.775%   $60.698   $60.70   $60.70   $60.70  
  Purchase #7 $177.68   5.490%   $187.4346   $187.43   $187.45   $187.40  
  7 purchase totals = $1,131.25       $1,205.8004   $1,205.80   $1,205.80   $1,205.80