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 $144.37   8.469%   $156.5967   $156.60   $156.60   $156.60  
  Purchase #2 $235.38   6.573%   $250.8515   $250.85   $250.85   $250.90  
  Purchase #3 $85.79   10.120%   $94.4719   $94.47   $94.45   $94.50  
  Purchase #4 $25.42   4.831%   $26.648   $26.65   $26.65   $26.60  
  Purchase #5 $209.31   9.623%   $229.4519   $229.45   $229.45   $229.50  
  Purchase #6 $101.47   9.309%   $110.9158   $110.92   $110.90   $110.90  
  Purchase #7 $106.91   6.676%   $114.0473   $114.05   $114.05   $114.00  
  7 purchase totals = $908.65       $982.9831   $982.99   $982.95   $983.00