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 $9.83   13.579%   $11.1648   $11.16   $11.15   $11.20  
  Purchase #2 $243.69   7.545%   $262.0764   $262.08   $262.10   $262.10  
  Purchase #3 $98.70   4.615%   $103.255   $103.26   $103.25   $103.30  
  Purchase #4 $25.83   4.791%   $27.0675   $27.07   $27.05   $27.10  
  Purchase #5 $241.88   9.584%   $265.0618   $265.06   $265.05   $265.10  
  Purchase #6 $59.67   7.835%   $64.3451   $64.35   $64.35   $64.30  
  Purchase #7 $43.61   11.220%   $48.503   $48.50   $48.50   $48.50  
  7 purchase totals = $723.21       $781.4736   $781.48   $781.45   $781.60