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 $218.83   10.694%   $242.2317   $242.23   $242.25   $242.20  
  Purchase #2 $159.72   12.323%   $179.4023   $179.40   $179.40   $179.40  
  Purchase #3 $148.33   5.362%   $156.2835   $156.28   $156.30   $156.30  
  Purchase #4 $154.49   6.192%   $164.056   $164.06   $164.05   $164.10  
  Purchase #5 $242.34   13.620%   $275.3467   $275.35   $275.35   $275.30  
  Purchase #6 $16.32   7.572%   $17.5558   $17.56   $17.55   $17.60  
  Purchase #7 $215.27   8.778%   $234.1664   $234.17   $234.15   $234.20  
  7 purchase totals = $1,155.30       $1,269.0424   $1,269.05   $1,269.05   $1,269.10