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 $160.62   11.606%   $179.2616   $179.26   $179.25   $179.30  
  Purchase #2 $239.29   8.276%   $259.0936   $259.09   $259.10   $259.10  
  Purchase #3 $147.64   6.740%   $157.5909   $157.59   $157.60   $157.60  
  Purchase #4 $88.72   7.368%   $95.2569   $95.26   $95.25   $95.30  
  Purchase #5 $201.87   11.687%   $225.4625   $225.46   $225.45   $225.50  
  Purchase #6 $18.39   10.573%   $20.3344   $20.33   $20.35   $20.30  
  Purchase #7 $122.57   11.685%   $136.8923   $136.89   $136.90   $136.90  
  7 purchase totals = $979.10       $1,073.8922   $1,073.88   $1,073.90   $1,074.00