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 $173.54   13.518%   $196.9991   $197.00   $197.00   $197.00  
  Purchase #2 $123.30   13.114%   $139.4696   $139.47   $139.45   $139.50  
  Purchase #3 $11.64   10.456%   $12.8571   $12.86   $12.85   $12.90  
  Purchase #4 $22.42   8.656%   $24.3607   $24.36   $24.35   $24.40  
  Purchase #5 $122.60   10.771%   $135.8052   $135.81   $135.80   $135.80  
  Purchase #6 $17.38   3.228%   $17.941   $17.94   $17.95   $17.90  
  Purchase #7 $61.81   4.439%   $64.5537   $64.55   $64.55   $64.60  
  7 purchase totals = $532.69       $591.9864   $591.99   $591.95   $592.10