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 $211.93   7.712%   $228.274   $228.27   $228.25   $228.30  
  Purchase #2 $207.87   8.179%   $224.8717   $224.87   $224.85   $224.90  
  Purchase #3 $187.32   13.210%   $212.065   $212.07   $212.05   $212.10  
  Purchase #4 $218.30   7.861%   $235.4606   $235.46   $235.45   $235.50  
  Purchase #5 $89.77   13.754%   $102.117   $102.12   $102.10   $102.10  
  Purchase #6 $53.48   12.182%   $59.9949   $59.99   $60.00   $60.00  
  Purchase #7 $200.79   13.655%   $228.2079   $228.21   $228.20   $228.20  
  7 purchase totals = $1,169.46       $1,290.9911   $1,290.99   $1,290.90   $1,291.10