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 $58.94   8.721%   $64.0802   $64.08   $64.10   $64.10  
  Purchase #2 $71.38   4.703%   $74.737   $74.74   $74.75   $74.70  
  Purchase #3 $218.85   9.396%   $239.4131   $239.41   $239.40   $239.40  
  Purchase #4 $57.95   4.422%   $60.5125   $60.51   $60.50   $60.50  
  Purchase #5 $156.25   4.614%   $163.4594   $163.46   $163.45   $163.50  
  Purchase #6 $220.73   13.543%   $250.6235   $250.62   $250.60   $250.60  
  Purchase #7 $173.39   12.710%   $195.4279   $195.43   $195.45   $195.40  
  7 purchase totals = $957.49       $1,048.2536   $1,048.25   $1,048.25   $1,048.20